Ok, I've posted this before, with no answer, but now I got more ahng of it and I know what the problem is. I can't find a solution though.
Once I install the mod, only one icon appears, which is the mod with the BI engine (or however it's called). I already have made work tons of mods with steam, just having to put a part of the target of the mods properties into a copy of the steam executable of RTW (in the target of the latter).
Although when I try to launch the mod, I get to the red screen (not the one with the loading bar) but then I get a CTD with a warning message that it doesn't support the horde feature.
So what I can get from this is that steam doesn't "read" that this runs with the BI engine, so it starts the mod with the RTW engine, leading it to not be able to use the horde feature. How can I solve this? It's already the second time I attempt to run this mod and I can't.
I've got RTW on the 1.5 patch, BI with the 1.6 and the RTR mod switch on 1.9 version (can't play it though due to many CTDs, seems that the pc is having trouble with it, it's really old)
thanks for the time spent on reading (and hopefully answering!)