Add a number to the pre-existing file, not the target file

I am looking for a command that will rename a file from oldname.oldext to newname.newext, with the proviso that if there is a clash with a pre-existing file already called newname.newext, this pre-existing file will first be renamed as newname (1).newext. The command:

Rename From oldname.oldext To newname.newext AutoRename

leaves any pre-existing file untouched and renames the target file as newname (1).newext, but I want things the other way around. I can omit the "AutoRename" so that I get an error message with a dialogue allowing me to choose which to do, but is there a command that will automate my choice?

The copy/move command has something similar, but to do it using the rename command will need a rename script, I think.

Thanks, Leo. I'm not up to scripting, but there's no great drama because with "AutoRename" omitted, I only need to press "E" for "Replace" — and anyway, it's not a frequent occurrence. Could I suggest that this option be considered in a future update, allowing a command:
Rename From oldname.oldext To newname.newext AutoRenamePreexisting