Why modify? Because, for example, I want to replace the encryption plugin with SecureVNCPlugin.
By broken I mean you can't run them. Any attempt to do so displays a "7-Zip - Unsupported Method" message followed by "Z-Zip - Unspecified error".
I've approached 7-Zip's creator with this bug, but he turned it back to you:
Probably they use some old 7-Zip code without LZMA2 support.
So ask them to upgade sfx code to new 7-Zip code with LZMA support.
So can you please do so?
What he means is that you use LZMA, so when 7-Zip modifies the files it uses LZMA2 despite you only supporting LZMA.
Someone already reported it happens with PcHelpware too.