I also skipped the part where the batteries were removed, it was easy to replace the trackpad with batteries still attached - I only had to lift the upper battery a bit. Thanks for the guide, was extremely helpful.
I succeeded with this guide and an upgrade kit from ifixit, however the sata cable was VERY VERY short and almost too short (way shorter then in the guide's pictures). a couple of extra centimeters would have made the process much easier.
besides that, thanks for the detailed guide. took me about 2 hours until the mac was booting from the ssd successfully.