Hi, this isn’t currently possible in the way that you described. I have moved your post to the Feature Requests forum, please consider voting for it!
There is somewhat of a workaround, which involves using the “Calculate and Compare” feature to generate a route string containing optimum altitudes, copying that route string into the Route field, and then fine-tuning any altitudes as needed.
Full instructions and screenshots are available in this topic: Ability to disregard specific step climbs in OFP - #2 by SimBrief
I will leave this feature request open to possibly add a way to resume optimum altitudes in SimBrief routes down the road.
Best regards,