Hi mate, I have some experience with this.
First of all in order to change the studs you’ll have to press out the hub, at which point you will also need to replace the wheel bearing.
Afterwards you can unscrew the abs ring and press out the studs.
Studs from Smart Car fit and are a few mm longer. I have included all information with part number is in this thread:
https://livetodai.com/t/rear-disc-brake-conversion-sirion-yrv-awd/2201
At a later date I installed super long studs, they were listed as being for a Ford escort mk2/Opel
Hope this helps