Shure say's you would be wasting your time. Apparently, the acoustic chamber behind the mic cartridge of a wired SM58 is not present on wireless systems. This chamber defines an important part of how a wired SM58 sounds.
The PG series wireless mics are considered entry level systems while the SMs are mid level. The SM series will have better frequency response, polar response, handling noise, transient response, etc.
Are you looking at swapping cartridges because the SM58 sounds louder to you? Shure currently has 10 RPW wireless elements (capsules) that are interchangeable with each other. But, don't assume that an SM58 wireless mic element will sound louder on a PG transmitter. It will not. Although the output levels for each specific wired mic model may be very different, interchangeable wireless mic capsules are "normalized" (by placing an electronic circuit between the mic capsule and the transmitter section) so their output levels are essentially the same -- that's what makes them interchangeable.
