I'll amend my comment about change. I would like to see the ability to select a different ball from inventory in practice rounds. Using the mulligan feature we'd be able to more accurately compare various balls for certain shots.. Also, it would provide another avenue for using up those pesky "last balls" that are cluttering up the bag beyond the current system of using them in CTTH or trying to break the hotel windows at St. Andrews with them.
It shouldn't be that difficult to program. First, check that it's a practice round. If that's true, offer the equipment change after each mulligan. Again, if the practice round check is positive, in lieue of the starter ball default, offer the equipment change limiting it to what's already in the bag after the loss of the last ball.