If you want to modify your grub.cfg of your written boot stick or want to access the partitions (adding extra.lzma from @IG-88) you can use a free portable tool.
- the grub.cfg is located in the folder "grub" on the first partition (15MB)
- the extra.lzma is on the second partition (30MB)
1.) Download MiniTool Partition Wizard Free Edition (portable):