If you're a lard arse/a very very good rider then it may make a difference in strength. But if you just do small holes you'll be fine. If it's just the look you want, don't drill all the way through the rim wall, just enough to make a circle of exposed metal. For everyone who says don't drill the join, if you're relitively at ease with tools and the way things work, you'll realise the majority of rims are pinned at the join. So the metal is extruded through a die, bent into shape, and 2 pins lock into each other at the join, leaving a gap between the pins. With the correct size drill bit you can drill in between these pins without any problem. Then you can use this as a valve hole, and drill the current valve hole to the size of the others.