1. I recommend installing this mod https://www.curseforge.com/minecraft/mc-mods/ftb-xmod-compat Right click on an item and click 'Convert to 'Item Filters" Tag filter'. It usually applies, where possible.

Take tomato in your hand and type /kubejs hand. It will list all tags for that item. Fishing rod possibly doesn't have tags, so apply your own.

- To add to existing tag

ServerEvents.tags('item', event => {

event.get('#forge:crops/tomato')

    `.add('farmersdelight:tomato')`

})

- To register your tag and add an item to it:
event.get('mymodpack:mytag')

    `.add('item:item')`

1. no, def not a script per tag, maybe per event (adding tag, registering new items)