As explained above, you cannot change the drill size for components globally. That is, without changing each component in the library. You have not said whether this is for commercial manufacturing or DIY.
If it is the latter, there is a work around that might help. There is a ULP called "drill-aid". That affects layer 116 only. You can set whatever diameter you want in that layer and it affects all holes. If 0.6 mm is the same size or smaller than all the holes on your board, they will then appear to be all the same size. The UPL includes instructions for reversing the process, if that is not what you want.
1) I use it to help center the drills, so I use a fairly small setting like 0.3 mm.
2) If your board is being manufactured, I am not sure whether the manufacturer will even look at layer 116.
John