If you still have the original dmg file then archive it in case you need it later. But no, many of us have had more than one version of LW on our comp's at the same time. I would generally add the version no. to the name of the program however. This helps me when checking out the betas. I'm not sure, but generally when jumping backwards from major versions it can corrupt your downld prefs. So don't jump backwards in versions unless you really need to. Perhaps backup things at issue before you update to be sure.

eg: jumping back from version 4.9.39 to 4.9.30 shouldn't make any difference. But jumping back from 4.10.x backward might. I know jumping back from other major released did corrupt the downld prefs. Such as 4.9 to 4.8.1 or 4.1.8 to 4.0.4 for example.