Guess you could do like I've done if for most riding you prefer the 12-25, just switch out the 12-36 and longer chain when you really need it, assuming the SRAM rd shifts reasonably well with the 12-25. Guess you'd have to see if its worth it depending on how often you'd want to do it, and how much adjusting of the rd is required....
Yes I'll probably do that. It's only a 10 min change to switch cassettes.
FYI the the mountain X9 derailleur doesn't have a cable tensioner becuase the mountain group has that on the shifters. On the road group it's at the derailleur, so to combine the road shifters with the mountain derailleur you have to install an in line tensioner somewhere.