No. Once you choose your custom portal URL during onboarding, it can't be changed.
Your portal URL looks like client.gethomsie.com/yourhandle. The same handle is used for your landing page (start.gethomsie.com/yourhandle). Pick it carefully when you first set it up, because Homsie locks it in after that.
⚠️ Important: this isn't something you fix by re-submitting your PropTX or ITSO VOW agreement. Those forms ask for your portal URL so the board can check it. If you entered the wrong one there, submit the agreement again with your real portal URL (client.gethomsie.com/yourhandle). That updates what the board sees. It does not rename your Homsie URL.
If you need the exact URL to paste into a VOW form, open Settings → MLS Boards, click Complete agreement for the board, and copy Your portal URL to submit.