Is it legal for a employer to change the pay of employees only changing which employees pay he wants to?

Answer 1

Yes. The only exception being that the employer is not permitted to make salary or employment decisions for discriminatory reasons.

Answer 2

Of course it is! Why would it not be??

Some folks deserve more as they work harder and do a better job. They should be rewarded for their effort; they bring more value to the company and are paid accordingly.