Writing metadata overwrites old metadata

G'day
I'm trying to switch to using DO to keyword my photos. It's metadata panel is excellent but has one charateristic that rules it out of my workflow. When I write keywords as metadata the previous metadata is overwritten.
For me it's not practical to keyword each file only once. I may do a wedding and have one hundred pictures keyworded 'bride'. I do this in one operation. I then keyword 80 pictures with 'groom' in one more operation. And fifty pictures with the keyword 'mother of bride'. You get the idea.
As it stands now I have to keyword each file individually. I've been using Adobe Bridge but that requires me to pick keywords from a list. If I want to keyword a picture 'Uncle Fred' I have to first add that to the list. After a few dozen weddings the list is unmanageably long.
Any ideas? Am I missing something? Or should it be on the wish list of future features?
thanks for your time
regards
Robert, Melbourne

So you want to add keywords to previous ones, without overwriting the old ones? I´m using following code to achieve that:
SetAttr META "tags:{dlgstring}"

Multiple items can be set using ";" as a separator. When adding further keywords, they should be preceded by a "+", otherwise
the old content will be overwritten. You can also remove items from the keywords list, using "-".

As abr says, you can use + to add keywords and - to remove them. This also works in the metadata panel.

Thanks guys but this doesn't address my problem directly. I can't write a command for every keyword I want to add. Each shoot will have maybe a dozen unique and new keywords which I'm not going to use again.
Is there anything I can use directly with the metadata panel?
thanks again
robert

Jon, just reread your suggestion and noted your comment about the metadata panel. Will try it tonight. thanks
Robert

Jon, just reread your suggestion and noted your comment about the metadata panel. Will try it tonight. thanks
Robert[/quote]
Yep, that's just what I need. Thanks again to both of you.
Robert