Several of the body vendors include scripts to change the shape of the foot to match the shoe being worn from flat footed to on tip-toes. But when the foot shape changes, the avatar is left hovering in the air, or sinking into the ground and the hover height needs to be manually changed to reflect the new food position. I suggest adding a new LSL command to alter the hover height of the avatar. Thus:

llSetAgentHoverHeight(key Agent, float Distance)

( edit to add a key field to the command. Not surf if it would needed or not. but the the behavior that if the agent key is not also the owner key that the command is either ignored, or an error is shouted on the debug channel )

The distance can either be a fixed value, or a relative value based on the current hover value. Examples.

When I stand barefoot, my hover height is "0.06" -- as shown on the "Avatar > Hover Height > Set Hover Height" slider.

But when I'm wearing heels my hover height is "0.170"

So the "llSetAgentHoverHeight" would either need to set the static values of 0.06, 0.170, and any other needed values for the shoes in question, or adding (+0.102) to the "current' value when putting on heels, and subtracting (-0.102) from the 'current' value when putting on flats.

The actual values, either static or relative would need to be established either by the shoe maker, or the shoe wearer, depending on how the script maker decides best of course.