Magazine Site -- Duplicating Last Issue

Four times a year we build a new site for the online version of our
university's alumni magazine. The structure is much the same each time. We use
three templates for each issue, one of which is just an admin template that
never changes issue to issue. The other two are only very slightly different
issue to issue... one says "Spring" the next "Summer" etc.

My question is whether I can copy our last site wholesale and then change it?
I'd need to make a copy of the whole thing and then isolate it somehow, rename
templates, have all the dependent pages update automatically, and then
reintegrate back into the architecture of the site. My worry is messing up the
issue I used as the master version. Is this going to save time in the long run?
I think so, but there may be complications I'm not anticipating. If there's
time to save, can anyone suggest how this might be done?

Thanks for your help. :confused;