Getting new visa after the current one expires

Hi,
I have a double entry permit and will have used both entries by entering china mainland then visiting Hong Kong. I now want to enter DPRK and come back into China. I know that I'll need a new entry permit and that this can be issued in Pyongyang but is there any restriction on getting a new one given I'll have already had over 40 days with the first one? I'm a UK citizen on a tourist L type.

regards
Marcus