I was wondering , if this be possible , can we make an adjustable electricty generator? If not, why so? Appreciate any responses .
Yes, it can. Indeed most dynamos use coils for both the stator (nonrotating part and the rotor (rotating part): a generator which uses permanent magnets for the stator is called a magneto (and anyone with a suitably old car will hate magnetos as much as I do!).
The trick these things employ is that there is some residual magnetism left in the iron cores of the stator even when the system is not running, and you can make use of this to essentially bootstrap the system: as it starts spinning it will generate some power as the rotor moves in the residual field, and this can be used to energise the field coils in the stator, and the thing thus bootstraps itself. This is called 'self-exciting' and that you could do this was historically an important discovery.
I'm actually not sure if there are generators which use rotating permanent magnets in any kind of wide use: other than not needing brushes I don't think such a thing would be very useful.