Flying Bull:
Hi Haroon,
It all depends ob your type of equipment.
Old school turnknobs - better switch to standby or you might transmit an emergencycode…
New ones - change is normaly possible without standby but its all written down in the appropriate documentation, which should be available to the pilot…
I started with 64 code transponders then after a few years we went to 4096 with Mode C. The company told us to never go to standby when switching codes. Instead, if assigned a code with a leading "7" use your brain to not select, 7500, 7600, or 7700.
Really not exactly rocket science.