The Arbookmarks package adds bookmarks to a recording where the Accurate Recording 'Start' and 'Stop' flags are found, so it is obviously possible, I would say it would be possible to add this as a feature of the hmt package, but it isn't there at present, unless it is an undocumented feature, the recording would need to be decrypted before bookmarks are added though I think. Also without being able to 'see' the point at which you wanted to add bookmarks, you would have to count seconds from the start in order to point to the place you wanted to add itIs there a utility to add bookmarks to a recording?
humax# strings hmt | grep 'book' display_bookmarks -bookmarks Display bookmarks. bookmarks
humax# nicesplice -in Titanic_20140430_1640 -out test -addBookMark 800 progLen = 6874s, 0 bookmarks, HD = 0 Read 171836 entries from nts ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Wrote 171836 entries to test. Stripped 2151752 packets (403453k) of EPG data New Program Length = 6873s
hmt +clearbookmarks file.hmt hmt +setbookmarks= file.hmt