[exim-dev] How to change a header from local_scan() function…

I would like to change the content of a message header from within a
local_scan() function. Apparently, there is no function in Exim for
doing that.

Is it safe to simply traverse the 'header_list', look for the entry I
want changed, and modify the slen and text fields there?

Cheers,
-Hilko