I've changed the title as it looks like it might be some time before we get a modding sub-forum.
SO the thread is now a place to ask sub-modding questions and place information.
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Original text of O/P:
Spoiler Alert, click show to read:
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One thing I've discovered (although Xeryx has posted on this some time ago but probably worth a mention) is the necessity to clear the cache when testing mods.
M2TW caches all the files in the SS6.3 directory for easy fetching during the game.
If you try and hotswop files without clearing the cache the prog, when running may use the cache version not necessarily the newer version.
Which can lead to ages to trying to debug something that actually works OK. (or lead you to think it does when it doesn't.)
One can remove the map.rwm between tests to rebuild the map (generally a good idea anyway) but this doesn't clear the cache.