I know how it is done but does someone have a trick for holding/pushing or otherwise capturing the hammer spring so you can line the plug up and put the pin back in. Holy cow my thumbs still hurt from exchanging the small for the large, but I would like to go down to the medium.....but I fear releasing that spring again

Does yours have the lanyard loop hammer spring cap?  If so, just (with the hammer forward) push down on a flat surface with the frame and it will take the pressure off the hammer spring cap and make the pin easy to push out.

If yours does not have the lanyard loop hammer spring cap then all I can recommend is putting a small nut (smaller in diameter than the spring cap) down on a flat surface, lining the frame up so the hammer spring cap is on the nut and then pushing downwards to relieve the pressure on the spring cap and make the pin easier to push out.

No lanyard loop, but the nut is a better idea than my thumb idea the last time....thumb hurt for days after that experience