change custom visual name

You can change the display name of a visual in the pbiviz.json file.  The displayName property changes what is see by uses when they hover over your visual in the Visualizations list.

{
  "visual": {
    "name": "snazzyTable",
    "displayName": "Snazzy Table",    "guid": "PBI_CV_B9C6C6C7_9583_4BF9_B2E0_9CE157681851",
    "visualClassName": "SnazzyTable",
    "version": "1.0.0",
    "description": "",
    "supportUrl": "",
    "gitHubUrl": ""
  }

Is this what you are after?

Ted is right... If for any reason you needed to bring any changes the custom visual name, displayName  or even visual class name , that would be done in pbiviz.json file of your project

{
    "visual": {
        "name": "CustomVisual", // internal visual name (should not contain spaces)
        "displayName": "Custom Visual!", // visual name displayed to user (used in gallery)
        "guid": "PBI_CV_xxxxxxx", // a unique id for this visual MUST BE UNIQUE
        "visualClassName": "Custom" // the entry class for your visual. (By default Visual: visual.ts)
        "version": "1.0.0", // visual version. Should be semantic version (increment if you update the visual)
        "description": "", // description used in gallery
        "supportUrl": "", // url to where users can get support for this visual
        "gitHubUrl": "" // url to the source in github (if applicable)
    },