How can I make a planning of a project that not changes when I fill-out the 'real work allocation'
You can't
Well sorry, for this provocative answer.
In fact you should not ...
The answer to the question is :
Only use some static planning mode (fixed duration for instance).
If planning mode is ASAP, and no work is defined, real work is taken as default.
But Project'Or RIA is not designed this way.
Project'Or RIA is effort driven : planning is based on work.
So you should define some work on activities (assign some work for a resource).
Define priorities, dependencies between tasks...
Then run planning : you get best planning depending on your constraints and resource availability.
Then, when resource enter real work
and re-estimates left work you can replan projet to get new target...