If it were only that simple 
You and Emmanuel have wright.I've tried to find a general formula but I've fail (until now).
A possibly workaround could be to have a specific prefix for fixed part (only one) on every adjustable model prefixed with sweethome3d_fixed_[part-name] like sweethome3d_fixed_exterior-frame
which could be used as references for YXZ.
I could also to add another custom property to roof windows and, to plugin, a deformation listener but this will produce a significant slowing of the entire program.
So, at that moment, I will let it as is.
With/Without this I'm wait the final 7.2 release to enjoy discovering the news
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A computer program does what you tell it to do, not what you want it to do. Murphy's Law
When all else fails, read the instructions. Murphy's Law
If you don't like "AS IS", DIY. Dorin's law
