When you have the timing belt set up on all timing marks ,Cams and crank then you remove the belt and make sure you don't turn the crankshaft or cam in any direction .
Then just fit the new belt , not sure what you mean by turning 50deg, but once the belt is remove there is no need to move any cams or crank shaft .
If any part is move then should be put back to where it was lined up.
Now if you are going to replace the three seals then yes you can move the crank back 30 deg to put the piston in the middle of there run, so not to touch the valve when removing the cam sprocket to replace the seal, when finished move back to TDC fit belts .
If you need a timing mark diagram please let me know i will post one for you.
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Kind regards Greg.