I made a copy of that in another folder called "perl5.8". Will this cause any issues?

Presumably yes, because - as I said - the original installation directory is hardcoded in the perl binary.

It's easy to check: just call

$ /path/to/your/copied/version/in/folder/perl5.8/bin/perl -V
[download]

If that still reports the original @INC paths (which I assume), it won't work.

Another way to check:

$ strings /path/to/your/copied/version/in/folder/perl5.8/bin/perl | gr
+ep /perl5
[download]

If you see the original installation path among the strings shown, it's hardcoded in the binary...

(In case you're feeling brave (and all else fails), you could use a binary/hex editor and modify those paths directly in the perl binary. This will only work, however, if the new path is the same length or shorter than the original one. If the new one is shorter, you'll have to put a zero byte (\0) right after the last character of the new path, without modifying the size of the binary (!), i.e. without deleting any left-over garbage after the new string-terminating zero byte.)