[Therion] Additions To Pocket Topo Data

Hi, If I bring Pocket Topo data/sketch into Therion with Top Parser and draw up the survey and then go back to the cave and add more stuff to the original topo file using say the continue here option is it possible to somehow easily get/replace the amended topo data into the original .th2 file and retain the scrap work already done or do I have to create a new survey. Obviously I can amend the .th with a text editor. I sometimes find myself waiting to draw things up whilst I get time to go back to get the last bits of the survey done so everything is in one file and I don't have to join it all together. Sorry if this is a bit of a stupid question but if you don't ask you never find out. Nick Bairstow