If you need to enlarge the holes, take it to a good repair person. The cost of the job is less than the cost of tool to do it right, and you do NOT want to use a drill bit. It is all but impossible to do it right with a drill bit.
The most important question, however, is WHY do you want new tuners. If you are having tuning problems, there is probably something else at fault. If you decide to get the higher ratio tuners, Gotoh 510s are the way to go, hands down. They are the best made gears on the market, in every way.
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"Cowards can never be moral."
M.K. Gandhi