Anyone can report anyone for any reason. Doubtful it will result in any punishment.
When you voluntary play Blind Pick, you should be expected to autofill all roles. For whatever reason you want to duo top (perhaps because you called it behind someone), if support is the only role left, then that's what autofill in Blind is. You can force your way and go duo top regardless, but then don't expect a good game if the team does not want to try that experience (you probably won't be punished for it unless you have chat toxicity).
You're not "forced" to do anything. But I can't imagine that would be a fun game if you force your way to the top and have to face a very unhappy team on top of most probably losing that game (your adc is fucked 1v2 and your duo top also fucked with being behind on cs and exp).