can pic18f66k22 and pic18f66k90 be used interchangably without changing PCB design ?
almost pin diagram is same
both have same features exept k90 has aditional LCD driver feature.
Correct. Apart from the Segment LCD features of the PIC18f66k90 they are virutally the same, PIN compatible. So as long as you're not using the Segment LCD features, you shouldn't have any problems.