This framework uses Content Patcher to designate custom particle effects to:

farmers wearing specific equipment or wielding specific tools / weapons
specific-named NPCs
specific-named objects
specific coordinates on a named game location

Since Content Patcher allows for its own customization, the above can be more finely-tuned to, e.g. time, day, season, etc.

Creating Particle Effects
Content Patcher syntax should be something like:

        {
           "Action": "EditData",
           "Target": "Mods/aedenthorn.ParticleEffects/dict",
           "Entries": {
               "aedenthorn.CPParticleEffects/heartCat": {
                   "type":"object",
                   "name":"Statue Of Endless Fortune",
                   "movementType":"random",
                   "movementSpeed": 1,
                   "frameSpeed": 0.05,
                   "acceleration":0,
                   "minRotationRate":0.05,
                   "maxRotationRate":0.05,
                   "particleWidth":11,
                   "particleHeight":10,
                   "fieldOuterWidth": 128,
                   "fieldOuterHeight":256,
                   "fieldOffsetY": -32,
                   "belowOffset": 0.001,
                   "aboveOffset": 0.001,
                   "minParticleScale": 2,
                   "maxParticleScale": 2,
                   "particleChance": 0.1,
                   "maxParticles": 20,
                   "minLifespan": 80,
                   "maxLifespan": 160,
                   "spriteSheetPath": "Mods/aedenthorn.ParticleEffects/heart",
               }
           }
       },
       {
           "Action": "Load",
           "Target": "Mods/aedenthorn.ParticleEffects/heart",
           "FromFile": "assets/heart.png"
       }

Don't change "Target", that's the mod's dictionary path.

The entry key must be unique.

Value fields:

type: the type of thing to target; one of "object", "npc", "location", "hat", "shirt", "boots", "pants", "tool", "ring"
name: the name or id of the specific thing of type to target
movementType: how particles move; one of "none", "away", "towards", "up", "down", "left", "right", "random"
movementSpeed: how many pixels a particle moves per tick
acceleration: how many pixels / tick the movement speed increases per tick
frameSpeed: how many animation frames change per tick (see textures below)
restrictOuter: whether particles disappear when they move outside the field (default false)
restrictInner: whether particles disappear when they move inside the inner boundary (default false)
belowOffset: if set to > 0, allows particles to move behind the thing by the given layer depth offset (default -1)
aboveOffset: if set to > 0, allows particles to move in front of the thing by the given layer depth offset (default 0.001)
minRotationRate: if set to > 0, allows particles to rotate around their center
maxRotationRate: if set to > 0, allows particles to rotate around their center
minAlpha: allows transparency (default: 1)
maxAlpha: allows transparency (default: 1)
particleWidth: the width of each particle on the sprite sheet (see textures below)
particleHeight: the height of each particle on the sprite sheet (see textures below)
fieldOuterRadius: if set to > 0, specifies a circular particle spawn field and sets the outer radius of the field
fieldInnerRadius: if set to > 0, sets the inner radius of the field
fieldOuterWidth: if fieldOuterRadius is set to 0, designates the outer width of the rectangular particle field
fieldOuterHeight: if fieldOuterRadius is set to 0, designates the outer height of the rectangular particle field
fieldInnerWidth: if set to > 0, sets the inner width of the rectangular particle field
fieldInnerHeight: if set to > 0, sets the inner height of the rectangular particle field
fieldOffsetX: for locations, specifies the X coordinate of the field center on the map; for everything else, specifies the field X offset from the thing's center
fieldOffsetY: for locations, specifies the Y coordinate of the field center on the map; for everything else, specifies the field Y offset from the thing's center
maxParticles: sets the maximum number of simultaneous particles in a field
minLifespan: minimum number of ticks a particle lives
maxLifespan: maximum number of ticks a particle lives
minParticleScale: minimum scale of each particle in the field
maxParticleScale: maximum scale of each particle in the field
particleChance: the chance (0 to 1) that a new particle will be created, checked each tick
spriteSheetPath: the fake path to this particle's spritesheet, caught by your Content Patcher pack (as in the example above).

Textures
Your sprite sheets should be created with frames horizontally and alternatives vertically.

So, say your particles are 3x3 pixels each, each particle has ten frames, and there are five alternative sprites to choose from for each particle, then your sprite sheet texture should be 30x15 pixels in size: ten frames across x five alternatives down.

The mod will choose an alternative randomly for each particle if there are multiple alternatives.

API
There is a SMAPI API you can use in other SMAPI mods. The methods you can access are:

        public void BeginFarmerParticleEffect(long farmerID, string key);
        public void EndFarmerParticleEffect(long farmerID, string key);
        public void BeginNPCParticleEffect(string npc, string key);
        public void EndNPCParticleEffect(string npc, string key);
        public void BeginLocationParticleEffect(string location, int x, int y, string key);
        public void EndLocationParticleEffect(string location, int x, int y, string key);
        public List GetEffectNames();

x and y are pixel positions on the map.

Notes
There's an example pack in the files section.

Technical
Requires SMAPI, uses Harmony.

Compatible with Mod Updater for automatic updates.

Code is at https://github.com/aedenthorn/StardewValleyMods.

If you want to complain or ask for help or help me test my mods, you can visit my Discord server.

A list of all my mods for Stardew Valley is available at https://www.curseforge.com/members/erinthe/projects.