If there is no difference in the base rig as far as key poses goes you can correct the key pose by laying a additive pose using Layered Blend Per bone.
Base theory is the the first frame of an animation sequence could be considered the key pose for that sequence. The key pose is usually derived from the skeletal assets as imported, usually in the A or T pose. The animation is then applied as an absolute value as to transform and rotation. You can change the key pose of the sequence by changing the “relative” rotation of of the “additive” pose before the final result.
The basics. Using the first pose in the sequence as the reference you would create a pose of the same character reposed using heels and assign it as an additive. With in your migration path, before final out put, you would add the additive to the Layered Blend Per bone targeted to the left and right foot, you might have to play around a bit, and since it is not absolute the rotations with be + or - based on the key pose that it is applied to. Same animations but makes us of a “corrective” pose so that all of the animations applied now adds the use for heels.
Another use is to say add different weapons to the same animation stream