I have been experimenting with one way to deal with the problem. The overall approach I am trying is to:
1) Design a route I would like to follow. I am using
brouter.de (the web interface)
2) Export it to a Google Drive folder I call GPS Routes (not an important detail, but just the way I do it)
3) On phone I import the specific route (more about this in a bit)
4) I make sure that route is visible and give it a distinct color and width (why will be apparent in a minute)
5) On OSMAND I create a few POIs. They are usually somewhere on the route I just created. For example if I have a big loop for a route, I might create one at a far point on the route, then also one at my finish point (same as start for a loop). Below I call them point A and B.
6) I favorite the POIs A & B
7) I have done all of this without actually beginning my trip
8) At beginning of trip I start navigation to point A. I do not try to improve the route that OSMAND choses.
9) At this point on OSMAND screen you can see the OSMAND route with turn by turn instructions AND you can see the route I picked
10) Occasionally I look at the OSMAND screen and if I have deviated from my route, I get back on it.
11) If it hasn't done so yet, OSMAND will eventually chose a route that is similar or same as one I picked (to point A)
12) when I get to point A, I then ask OSMAND to navigate to point B
Regarding #3. I actually do this for many routes. I call them segments. I am a cyclist and have many favorite routes to take. I am building up a number of medium size segments that can be thought of as a web of routes. My intent is display the entire web on my phone (or sometimes just a subset of it) I haven't yet, but might choose to color them differently.
Regarding POIs. I actually create many of them that serve as nodes in my web.
This is not automatic but does solve the problem that I had in which I want OSMAND turn by turn, but I do not want to have to plan my route on OSMAND. It is good enough for me if I can have OSMAND plan to go to some point I choose and display for me the route I would like to take. In my case I don't mind getting off course a bit as long as I can see where I would like to be and have OSMAND try to get me to my destination.
I have not included specific instructions above, just "psuedo instructions". I can provide details if there is an interest. I can also give some renders of the POIs and route segments.
I am a cyclist doing rides from 10 mi to 50 mi who wants various routes to choose depending on my mood.