Change disbursement to 1 payment a month rather than 2

Not that I know of.

Its fortnightly by standard, or as you manually request.

I would warn against leaving too much funds in there though, if Amazon decide to suspend your account, or put you under review (which they regularly do without reason or warning) they will put all your funds on hold until they sort the problem out (and since that is having a conversation with Seller Support you know how long that could take…)