I play in a vocal-led covers band. We are two vocalists, myself and a drummer. We have no bassist. I play a Taylor 414 with a Fishman sound hole pickup through a Roland AC60 which I use to shape my sound, then run a line out of the Roland into our mixer/PA. I dial in some extra base frequency on the Roland and mixer and use my style and strumming dynamics to provide both a bass line and a 'normal' guitar accompaniment. Understand the set-up sounds a bit weird, but getting to this stage was a happy accident and it works nicely 95% of the time as it gives us a really nice unique sound. But I do have the one issue - sometimes when I use a capo to play in the right key for the vocalists, I lose a lot of the bass frequencies as I'm playing higher notes. The answer is easy - an EQ pedal. But sometimes I need to diall-in more AND roll-off the bass frequencies DURING the same song (e.g. in a song played in E: the E-chord works great, lots of bass frequencies even with a capo up on the four fret, but the A-chord is weak). Switching between two settings often during the same song just wouldn't sound right, the difference is too unsubtle (easily get away with this with solos but not with chords). So what's the answer? An EQ pedal with an external expression pedal (EHX Tube EQ the only one out there) for smooth transitions? Or anyone got any other ideas? Be very grateful for any suggestions. Thank you.
It should work but I think this is something you are going to need to test on your own since your set up and situation are pretty specific.
Will kinda work, but you won't be getting the effect of a bass- you'll just be getting a 'boomy' sound, which may be exactly what you want, or it will sound hella muddy. Only way to know is to try it out I guess. Two EQ pedals may get the effect, but still slightly unsure what it would acheive.

Another way to fill out your sound would be to get something like an octave pedal (Nano POG or something) on its own or the Submarine pickup through a pedal to give you bass notes either over all strings, or just the lowest two, to provide a bass sound without being over boomy.
I have seen a solo artist use an Graphic EQ peddle for more bass, can't remember who it was. He simply had a 7 or 8 band EQ with the bottom fader at max, the next to bottom at min and the others set to a smile.

A couple of tricks you might try, if you can get more action under the bottom string (use one of the superglue and powder trick to fill in the nut slot, then you should be able to get the bottom string down to A - making the new chord shapes fairly obvious. Another trick is to use a 5 string partial capo, giving you an C, D, or E bass string even with the capo on.