If I understand correctly what you are trying to do it means that you want to concatenate G54 and G55. That's not possible because both frames can't be active at the same time.
But you can concatenate other frames. One option would be to keep G54 active and selecting your specific part by using TRANS in your NC-programme. With the values in your example:
TRANS X0 Y0 Z25
When you want to go to the next part you just write the new offset in a block with the same syntax.
If you want to change your offset incrementally replace TRANS by ATRANS for example:
ATRANS X10 Y10 Z0