Built a bathroom onto our office and need to run a switched line for bathroom ceiling light and exhaust fan. For simplicity's sake, looking to pull power source off the end of a line already on a switch. The already established line powers two ceiling lights in the office and I understand that this line needs to be switched on for power to go to bathroom. This is fine, nobody will be using the bathroom unless the office is in use anyway. Just want to know if this is okay. Thank you!
Electrical work should really be done by a licensed Electrical Contractor. Please only undertake DIY wiring if you REALLY understand what you are doing.
What you are suggesting is not ideal, and should be avoided if possible.
How are you planning to switch the new fittings? Sometimes, for example when retrofitting say an exhaust fan to a bathroom or WC, there is no access, and the only way is to tap into the light, generally using a pull-cord switch. Not ideal but sometimes unavoidable.