If you TASO to an inf unit it may be possible, although i would suspect it would only happen post commissioning. Until you get that far get yourself on MOD3. Depending on the RTC they can be quite full on, although i would steer clear of OTC ones.
Nope! Nada! No chancio! If you're not commissioned, then you wont get on the Platoon Commanders role. Why not try to go for Juniors? Then you could maybe wear some tapes at your OTC, that would make you a ninja-like god!
The OTC is not there to craft infantry platoon commanders. The OTC is about developing leadership, and there are plenty of more effective (and cheaper) ways of doing it than going to Brecon. If you are really set on going and have the relevant experience than go and have a chat to your adj, but i would bet a significant amount of money he will be of a similar opinion.