I'm in a similar sitch to you - needing to work out thr financials and protect myself, but ideally not wanting to D. My L has suggested we work towards a deed of separation along with a financial settlement. Whilst it is not a watertight document, she advised me that it carries significant weight with the court in the event that we do ultimately D.
How she described it was that the deed would normally carry through and be part of the D proceedings - as you say unless something changes in the meantime. But my L said that the 'something' would need to be substantial. The example she gave was if one of us had a serious accident and were no longer able to work. She said the courts would take a pretty dim view of someone trying to change something that they agreed to, having had legal advice, unless there were a significant factor in there.
So, at the moment, H and I are working towards a deed of S, and I hope that we may either be able to reconcile or that we may D once the 2 year separation period is up.
T 13 M 7 Me 48 H 46 SS 15 BD 7.14 PA D final 5.16 (H filed)
We receive & we lose, and must try to achieve gratitude & embrace with whole hearts whatever of life that remains after the losses - Dubus