Butter fingers,
Never yet heard of a decal limit as such - certainly there are both AI script and map object limits. They both cause a game or level to fail to run and return fatal errors though in dufferent ways
The only option in these instances is to remove something to reduce below the limits.
If there is indeed a decal limit then this needs someone to fully confirm this and it needs to be reported in the bug forum or otherwise it is never going to get fixed - hopefully in time for any update.
I have not had that problem of a decal limit as such - I have had decals fail to work though - through erratic FPSC behaviours and eventually got them fixed by recreating decals and saving out the image files and redoing the scripts until I got them to work correctly. I had in my instances to repeatedly delete the .bin and .dbo files many times while doing this in an attempt to get FPSC to recognise the new versions of the decals.
Decals as with any other entity may fail to work correctly and behave erratically and stop animating or working (responding) if a level becomes over complex.
FPSC can get itself in a tiswas sometimes and in its confusion get locked in a spiral of continual misbehaviour of entities as it can get stuck in that state - when it apparently fails to update a level map file. Sometimes deleting any associated temp files - rebooting and and so on can get it to reset itself.
I have had many such problems in the past and have had to get nasty with FPSC to crack some issues of that kind - gone those days are thank goodness.
I am not sure that decals can be deactivated at all - much of how they work is written into and controlled exclusively inside the source without any user control - which is why we have such difficulty in obtaining any over them.
As being an important question - How many decals total do you have?
Not sure that it matters but do you know how many entities of differing kinds you have and how many entities total you have? I have nearing 600 entities in a single level - that does not exceed any kind of limit yet. The map object limit seems to relate to segments and not entities - where you have to watch the script limit instead.
Whats the total number of AI entity scripts in the combined scripts folders inside FPSC? 200 is the max so anyone that has more than that is going to come to a stop. That will include all scripts whether default ones - those you may have created yourself or any that have been installed from purchased or free content packs. 200 max is your lot.
It sounds to me like as if FPSC has just gone a bit haywire with you thats all - thats all! LOL!
Thats all I can suggest not having come across a specific decal limit - have a think and look see if any of the other things I mentioned could cause your probs.
Hope you get it sorted soon
"I am and forever will be your friend"