As of the 1.14.4 release, PNC:R has moved to using Datapacks for all recipe customisation, as well as for Amadron trades and block heat properties (e.g. the definitions that make Magma blocks able to fuel a Refinery). You will need to be familiar with how datapacks in Minecraft 1.13+ work to carry out any customisation, and the linked document is required reading.

To customise recipes, create yourself a datapack:

• On dedicated server, the pack will be in <SERVER_ROOT>/world/datapacks/<PACK_NAME>/
• On single player, the pack will be in <MINECRAFT_DIR>/saves/<WORLD_NAME>/datapacks/<PACK_NAME>/

PACK_NAME can be whatever you choose; you can add multiple datapacks too, if you want.

In both cases, the datapack folder should contain a pack.mcmeta file that looks like this for 1.14.4:

{
    "pack": {
        "pack_format": 4,
        "description": "Any text you like can go here"
    }
}

or this for 1.15.2:

{
    "pack": {
        "pack_format": 5,
        "description": "Any text you like can go here"
    }
}

and for 1.16.x:

{
    "pack": {
        "description": "Any text you like can go here",
        "pack_format": 6
    }
}