I've seen many people talk about trying triode mode for output tubes, and I've never seen anyone say they liked it. It may be good for hi-fi, but not for guitar amps.
You could certainly try it out and report back to us.
My 50W ODS (HRM) built by a local tech has pentode/triode switch. Volume and headroom is not extensive. For my bedroom playing I just turn the amp down on pentode operation and sounds fine. Tonewise, triode mode is to me a little thinner. Not bad, but I just prefer the pentode operation.