From experience, but then again it was a long, long time ago and you reminded me that I would need to exchange some coins to notes soon...the branches normally recommend that you go to their Head Office in Hong Kong, if not, they should or you can ask them which branch/HO you can take your coins where you do not have to pay for administration service.
I had to go to Standard Chartered Bank Head Office in Central to do some exchange few years back.
Or, what I do sometimes is take some coins with me and use that the whole day to pay for lunch, Octopus, etc...shops love them. Some even asked if I can do some exchange with my coins to their notes.
Good Luck
