While he's speaking of blending two pickups instead of caps, you may have significant loss of output at the center detent if it's not a "true blend" pot.
Also, you now have a switch, so you either have one capacitor or the other. With a blend control (and again, assuming the caps are in parallel), you'll be adding the values of both caps together as you twist the knob. (This may mean selecting different cap values to get the sound you want.)
Another question arises, too: Is there a "no cap" setting with your current switching arrangement, and how will you maintain that option with a blend pot?
Please understand that none of this is meant to discourage you from experimenting, I'm just raising some things for you to consider. I believe we have had a member or two try something similar to what you're asking, so I'll have to look through our dusty basement to see if I can find that thread.
Couldn't find the thread of which I was thinking. Most of these "cap-switching" ideas have been done in conjunction with a tone pot, not "free standing" as I have assumed you are doing. If my assumption is wrong, here's some links to ideas for multiple tone pot caps:
Based upon what you're requesting, can I assume that these caps are wired to ground, in parallel with the output?
Yeah. I could get some interesting tone variations that way.
I'll have a good read of the link before I do anything. Although I might just see what happens- it's only a few bolbs of solder As I remember the pot allowed blending of the pickup tones when both were on. It had a master tone and a blend. I suppose it functioned in the place of 2 tone knobs that way.
I may put in a tone bypass switch too. I have 3 mini toggles but now have non coil splittable active pickups so the redundant switches are sat staring at me with no wires on them. Before I had coil taps and phase reversal which I never used to be honest.
I'm thinking of something more straightforward but with as much tone variation as I can get.