I'm hesitant to agree that merely exposing the sensors "breaks" tracking. I (very carefully) disassembled one of the controllers to re-seat a loose haptic motor and notice no difference in tracking accuracy or precision. The controller may be offset by some minute, imperceptible amount but it hasn't produced any problems. I think you would be fine attempting minor repairs with the appropriate amount of caution.
See this thread for a mod that replaces the foam gasket with some thin material from a sleep mask:
Mechanically reducing eye relief doesn't appear to be possible without heavy physical warranty-ruining modification.