Is it possible? I want my breloom to learn spore, but i didn't realise at the time that it can only learn it as shroomish...

No, devolution is not possible.

If I may suggest, try breeding a male Pokemon that knows Spore with a female Shroomish (Paras and Parasect both learn the attack if I recall, and I know they breed with Shroomish). Hatch the resulting egg and the Shroomish should know Spore, then you can evolve it whenever you please (after it reaches the minimum evolution level, of course).

-Gardevoir~

Incorrect. For the baby Shroomish to know Spore, the mother Shroomish needs to also know Spore, because Spore is a level-up move, not a TM or breeding move.

Youll have to catch another shroomish

Both parents do need to know the move. However, it's probably easier just to catch another Shroomish and evolve it after it learns Spore, rather than level up 2 so you can evolve it at the lowest possible level. You could give the Shroomish an Everstone so it won't try to evolve until you want it to.

I have a question! If its possible even, how do you evolve a pokemon after it would normaly?!?

every time a pokemon gains a level, if that level is above the level when it normally evolves, it will try to evolve again.

If only it was as straightforward as getting a new one! Alas, i have already given the current breloom a TM that i hoped to keep... i have the same problem with my entire team, all have the absolute worst natures yet i have constructed their movesets using some one off TM's... oh well, thanks for the advice!

i never realised this. i once bred a male breloom which knew spore and was surprised that the baby didnt know it. is that really right? i thought it was only the male parent who had anything to do with moves that pass on.

the male only passes on TMs and egg moves; both parents must know the move for moves learned by level up

Hey I think that the TM that you thought it was Focus Punch. If your playing Emerald you can use pickup to get it

It would be a good feature if it was true. You could de-evolve your pokemon so they could learn serten moves, and then evolve them back.

you know evoles to at lv 30 mine at lv 37

Mod Edit: That's completely irrelevant, and yes, pokemon will evolve into their next form at and level after the one they evolve at (IE, if it evolves at level 20, it will also do that evolution at level 21 if it doesn't do it at level 20 for some reason.)
-JsX™