[mkgmap-dev] Reserved codes for custom needs?

Hi List, I'm just working on a specific style which shall help me mapping some details when I walk around. E.g. I'd like to have an icon for traffic_signals and different icons for emergency_phone/telephone and different icons for post_boxes with collection_times and without collection_times. Otherwise it's really difficult to see whether I have already tagged some details or not. I've searched the current cGPSmapper-UsrMan-v02.5.pdf for assistance but could not find any codes which I can use for custom needs. Question: Will I get problems if I use codes which are not listed in the document or is this just unknown? Or are there even codes which are reserved for custom needs? Any help welcome Andre