It’s not clear to me that there’s a compelling reason to have a “one robot throughout the season” rule. Why not let teams iterate as much as they want, including building an entirely new robot?
I think taking this year’s set of rules and removing just those that require the robot to be bagged and tagged leaves a viable set of rules. C5, R5, and I3 still limit the team to a single robot within the course of an event, so a team couldn’t swap between robots as fast as they could get inspections done (as done famously by 1519 in 2008).
That said, without the 155lb rule you propose it’s somewhat of a gray area and up to the mythical “reasonably astute observer” where the limit is regarding getting reinspected after changing mechanisms versus having two distinct robots at the event. On the other hand, it’s become relatively commonplace for teams to pack spare assemblies in their bags as backups, and going down to 30lbs of backup fabricated assemblies could be a significant design constraint, especially if there’s heavy defense again.