I want to replace a small straight with a turnout and try not to damage existing turnouts. Track is pinned and I don't want to damage bend the existing fish plates.

Is the point an exact replacement for the plain track (same length)? What type of track is it - Peco Setrack?

With flexi track you can usually slide the fishplates all the way to one side to free up the section of track, even if you have to temporarily cut and remove a sleeper or two (these can be replaced with the special replacement sleepers Peco sell). With Setrack the fishplates are kind of spot-welded to the rail.  To be honest I would use a screwdriver and snipe nose pliers  to bend away and sacrifice the fishplates - you can always replace them.

If the plain track is longer than the point then I'd use a cutting disk in a minidrill, or a razor saw, to cut and remove a piece of track the same length as the point you want to insert.  Then slide fishplates all the way onto the remaining plain track, fit the point in the space and slide the fishplates back across.

Nick beat me to it

Is it possible to slide the fishplates completely onto the adjoining track with a pair of pliers if necessary (you may have to slice off a chair or two with a modelling knife to do this) such that you can lift out the straight, drop in the point and then slide the fishplate back to half and half, if you know what I mean. This will not work if you need to fit insulated rail joiners anywhere I'm afraid.