Can a 12-25 cogset be changed to 12-27 easily?

[rebeccaC]

YMMV, but IME there's not much "just" about replacing cable housing.

When you cut cable housing you have to (1) make sure you don't crimp the housing when you cut it, (2) use a smooth punch to open up the hole when you inevitably DO crimp the housing, and (3) file all the burrs off the cut end(s) so they don't catch and fray your cable.

Oak, I use a dremel with a cutoff wheel on both cable and housing. The dremel also has a thousand other uses unlike a park, felco, pedros etc. cutter. Eye protection, a steady hand, some tape on the cable and a piece of old cable in the housing where you cut makes it fast and easy to get a clean square cut.