Yes, it would.
Two rules of thumb:
a) don't do things to assets in use by Encore outside the program.
b) when replacing an asset change the name.
For example, you decide to edit part of the content. If you are using an all adobe content, use "edit original." If not, make the change, but when exporting from the source program, change the name. then, from within Encore, use "replace asset," and select the new asset.
I think you can still do this. FYI, some programs (e.g. Premiere) may use "sidecar" or other files which use the source file's name. You can't always just rename the file and expect all to work. If that is not an issue, just change the name, reopen encore, the file will be offline. Use replace asset and go find it. (Not where I can check. I don't recall what options encore has to find a source file - rather than located a transcoded file.) but replace is the safer move.
While drive letters are not an issue on a mac, there are issues regarding the use of external drives and also with permissions.
