There's no reason you can't work on the rigging with the mast up, its just not too convenient and you need to be careful when putting someone up in the air. With any common sense your mast won't fall down...don't release the uppers and lowers on the same side at the same time..either set will hold the mast in place just don't go sailing...
PS - I've never seen an adjustable spreader...
I've only seen adjustable spreaders on very small rigging. I think some dingy sailors are able to adjust their spreaders fore and aft.
It sound like Eihli is describing spreader boots to me but I could be wrong. I would suggest that he speak to some knowledgeable people on the dock. There are always "experts" around.
Eihli, get lots of opinions from people around the marina and then, just like with the center-board, check it out for yourself.
It's really not much more difficult to climb to the first set of spreaders than it is to dive under your boat and feel around.
You need to investigate, learn about and come to be familiar and comfortable with most if not all of the systems on your boat.
In order to be a competent and confidence inspiring skipper who will have all those bikini clad admirers clamoring for the opportunity to sail with you,
you need to be a hands on - get your head into it kind of sailor.
We are glad you came here and are glad to help.