[boost] [spirit][karma] In-place modification of previously parsed content?

Hello, I wonder if it is possible to modify previously parsed content using Karma. An example is some text like: coordinate (1, 4.15, 1.49, 0.81) // some comment 1 coordinate (1, -19, 4, -1) // some comment 2 Now suppose the numbers are all parsed, and I change the 0.81 to 71.44. I want to update the text accordingly: coordinate (1, 4.15, 1.49, 71.44) // some comment 2 coordinate (1, -19, 4, -1) // some comment 2 Note how the overall formatting and comments are preserved. The text could contain lots of other strings etc. and they would be all left untouched. This part - the preservation - is the hard one, and I ask, is this possible using Karma?