Python scripts that'll help you to nearly fully recover your NSIS-installation scripts.
It's currently in the 'alpha-state' however it's not far from being worth to title as beta or release.
I'm new to Sourceforge - for small updates I may also prefer the page below.
UPDATE: It'll maybe not working on this anymore. http://7-zip.de does a great job in also decompiling NSI.So I recommand you to check out 7-zip BETA.
Generally 7-zip opens NSI[exe] files - since 9.33 [2014-06-15...