can you alter whether a sample is stereo or mono after recording it? my synths tracks are hard panned left

Yep, by resampling it.

Press [resample] and then [rec]. Press the [stereo] button so it isn't lit and then select the pad you want to record the sample to, and hit the [rec] button again. Now all you have to do is play the sample you are wanting to make mono and it will go to the pad you selected earlier.

I do this all the time, generally converting stereo kick drums to mono to free up polyphony!