I'm not even sure it would be legal to leave in a solid slug where the current weight hole is. Would it be considered a foreign object if it wasn't going to be drilled? Why not just have the pro shop plug it as they would for any other hole? Then you could drill another weight hole anywhere you wanted. I'd guess you'd want a P4 "double thumb" weight hole to increase the dynamics. You'd get a bit more flare and more reaction down lane. It can make a fair difference, but don't expect a night and day difference with any weight hole.
I'd guess only a ball designer could make a good guess as to exactly how much the RG value waould change, not that I'd worry about it too much. Exactly where the current hole is in relation to the core shape and densities would be hard to estimate.
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Telling it like it is.