If a cab is so far gone that lifting one corner 1/4" higher than normal to replace a mount would compromise the integrity of the entire cab, then it would indeed not be a good idea to do so. If the cab is that bad, it would be a better choice to look for another cab entirely.
If you loosen both front cab bolts, the rear cab mounts design (either dual shackles, or center pivot mount) will allow a relatively large amount of lifting of the front mounts without torquing the cab at all.
Carl
