I want to put the 'Object limits plugin' by Neiv on a Mod made by someone else. I tried using FG 0.93, opening the mod with it, inserting the plugin, but whenever I save the changes the mod loses data. Is there any alternative way to achieve this?

What do you mean with the mod loses data? It should not. So maybe we should be diagnosing that instead.

Might wanna try MPQDraft but afaik the object limits plugins might rely on some exe edits by firegraft.