TSGL: Subject Headings in Thunderbird

[Trio800_BonBon]

Does anyone know how to easily change the subject line on  RECEIVED  
emails.

I get newsletter emails that  I sometimes save but  I would like to 
change the subject line to reflect the topic.

So far the only way I could find was to edit as new, save as draft and 
them move it back into the desired folder.

There's got to be an easier way. I used to use pocomail and you could 
just right click in the subject line and change it.

Thanks

Bob