No, Your 2000 Honda XR100 does not use this style chain adjuster. You can find the chain adjuster for your bike in the OEM diagrams here: http://www.motosport.com/dirtbike/oem-parts/HONDA/2000/XR100/REAR-WHEEL
Yes. This would would for a Honda CRF150R. They are a bit longer than the original adjuster bolts. These show M8x50mm bolt size, where as Honda shows M8x47.5mm bolt size (SKU# 90105-MEN-000). So these bolts would be 2.5mm longer than the OEM Honda Chain adjustment bolts, the extra length should not be an issue though.