I have an idea but before i run with it I need to know if you heard of a show going from, let's say, drama to fantasy. I have smooth transitions from one to the other and the B-plot carries through. The only changes are the characters and the A and C-plots. I think it could work but I need more opinions on this.
It will be risky, as long as fans know it is the same show. If not, you are essentially just creating a new show under the same name. It will also be difficult and if this show is one that lets writers have one or two chances at scripts before they move on to new talent (As some shows do) then you probably won't have the time to pull it off as you will need to slowly bring in the new era of the show, instead of just forcing it upon fans.
They do it for know entities, they would NEVER trust an outsider to do it.
99% of the reject pile, most of it un-read, is from spin-offs of pre-existing movies or shows.
They are taking a big financial risk with newcomers; they don’t want what their average trusted minions can produce.
In other words If you ARE IN you can as mediocre as you want, but if you WANT IN your ideas, and execution better be stellar.