you will need to order 2 extra of the spacer kits and use all the spacers in addition to the spacers that are included if you are trying to use a 100 mm motor on what is most likely a much much smaller bottom bracket shell. Personally I do not recommend doing this, it makes a lot of sense to get the right motor to begin with because it will affect your chainline which may cause chain derailment when you have it in certain gears. The exception to this might be if you are using an IGH on the rear.
https://electricbike.com/forum/forum/knowledge-base/motors-and-kits/bbshd/10736-how-to-order-the-right-bbsxx-kit this is a pretty good starting point
You will need pretty much every extension.
This has basic installation instructions, make sure to watch the videos https://www.reddit.com/r/ebikes/wiki/bbs_faq
good luck, and if there is anything we can do to help just let us know. For further build advice I recommend visiting our forum https://electricbike.com/forum/