Any utility that assists in the creation of mods, assets, etc, go here. For example: Ultimate Doom Builder, Slade, WadSmoosh, Oblige, etc.
Forum rules The Projects forums are ONLY for YOUR PROJECTS! If you are asking questions about a project, either find that project's thread, or start a thread in the General section instead.
A very small utility for mass editing vertices of the UDMF map (and copying+offsenting them and sector heights) . Currently doesn't support line specials, or things. https://github.com/smoketh/UDMF_VertexTools
Spoiler: workflow
Workflow boils down to this:
Create UDMF map in gzdoom builder.
Import OBJ as terrain.
Save the wad.
Open it up with slade.
Export textmap.
Open it in this tool.
Perform what you need.
Save.
Replace contents of textmap in wad and save it
Open in in gzdoom builder again.
Finalize and either export as prefab or start working on it.