To activate the different layouts depending on the preference, just replace the _manifest.ymf. It comes with a freeroam layout by default.
The folders are labeled for which layout you want.
There's currently (as of v1.0) 4 layouts
- 6KM
- 6KM Oval
- Junior
- No Layout (Freeroam)

FOR SINGLEPLAYER: Use OpenIV or Codewalker RPFexplorer, go to the dlc.rpf from the mod; navigate to x64 > levels > gta5 > monza_66_metadata.rpf
Replace the manifest in that rpf.

FOR FiveM: Replace the manifest inside the stream folder. Do not use multiple manifests at the same time, it will end up using all the layouts at once.