Update: Read and write support for .LSF files was added to the latest EE tools (beta, naturally)(
https://dl.dropboxusercontent.com/u/32263228/dos/gr2/ExportTool.zip).
There is not editor UI yet, but you can edit almost everything if you export the .LSF into .LSX (XML) format, edit it with notepad or something, then reimport it and resave as .LSF.
Some observations:
The v13 package format and the LSF files seem to be "write-optimized", ie. they are structured in such a way that the writer will be able to continuously stream data without having to seek in the output stream or do costly offset recalculations which were needed for the v10 packages and .LSB. This was probably the main reason for creating these formats.
In the case of PAK, the headers were moved to the very end of the file (so they're effectively "footers").
LSF uses multiple separate streams that are written to simultaneously and are concatenated into one large compressed blob in the final pass.
