If you are using a rapier with the feat Weapon Finesse while attempting to disarm an opponent, do you use DEX or STR on the CMB for the disarm attempt?
If I have Weapon Finesse, can I apply my Dex bonus to my combat maneuver checks instead of my Strength bonus??
It depends on what combat maneuver you’re attempting. Disarm, sunder, and trip are normally the only kinds of combat maneuvers in which you’re actually using a weapon to perform the maneuver, and therefore the weapon’s bonuses apply to the roll. Therefore, if you’re attempting a disarm, sunder, or trip maneuver, you can apply your Dex bonus instead of your Str mod on the combat maneuver check (assuming you’re using a finessable weapon, of course). For other combat maneuvers, you use the normal rule for determining CMB ( Str instead of Dex).
The Agile Maneuvers feat applies to all combat maneuvers, not just disarm, sunder, and trip, so it is still a useful option for a Dex-based creature that uses combat maneuvers.