After creating one and linking it to an s3 bucket, it is no longer possible to share this storage namespace with another lakeFS repo. If I don't use this repo anymore and I delete it, is there any way to connect a new repo to this same bucket ?

Unfortunately not all of the state of the repo is held on the storage namespace, so this is not possible. We would have the objects and the structure of contents of each commit, but AFAIK not the actual branches and commits.