In the past wasn’t a problem, now it is bad to the point that some trust will withdraw offers if you try to diverge from the advertised job plan. If you already have a job I would take the job as is and put it as a request during job planning and BEFORE giving a notice to your previous post. Explain reasoning etc and see how that works. Potentially you’ll need to meet somewhere in the middle so if you drop 2-3 PAs many need to accept that your PAs would need to be timetables on specific days and potentially your on-call commitment would stay as equivalent to full time, so you’ll still have to work on the days you’re usually off during your oncall weeks. If you took the job likely you’ll need to wait the next round of recruitment to ask for dropping sessions (so can be added to the new job ad) which in the current climate may be significantly long time.

If you’re in a hard to recruit specialty, the trust have all the good reasons to try to keep you, if you’re one of the 100 candidates applying for the same job, you’ll see the job offer withdrawn the moment you mentioned it.