Maximum N1 for CF6-80C2B...
 

Hi there! Can somebody clear up the matter. What do you think about Maximum N1 indication (yellow line) at engine parameter display, is it equal to Maximum takeoff thrust for ambient condition?

Yes, correct, but not specifically related to takeoff.
It is derived from the respective engines EEC and indicates the maximum thrust that the EEC has computed it can deliver (based on current ambient conditions) if you advance the thrust lever to the full forward stop.
The EEC is computing this at all times so the yellow bug will move up/down as conditions change.

Note: you didn't mention aircraft type but my experience is 767 installation.

So to clarify....the maximum N1 engine rotation speed in terms of rpm varies and is not a fixed value?

The max rated N1 is a function of altitude, Mach, and temperature (corner point and the square root Theta term), and of course the engine rating. Boeing has five CF6-80C2 ratings on the 767 - B2, B4, B6, B7, and B8 - and two on the 747-400 - B1 and B5. With the exception of the B8, the engine build is the same regardless of rating. Then just to make things more complicated you have FADEC and PMC (not all those ratings are available on the PMC).
Redline N1/N2 is fixed and never changes, however there can occasionally be some subtle changes in rotor speed redline values between different engine ratings.

Much clearer now, thank you!