Hi! In my years of working i have stumbled accross a lot of HDD drives that has partially damaged, have Scratches on 1 of the surfaces

I have recovered many cases that the heads of the drive got dead, however i have little knowledge and skills to do partially damaged HDD.
SO
I am here asking for everybody's help sharing that knowledge. Like how to physically cut the heads? How to cut heads in ROM, what to modify in ROM and RAM. How to do a hot SWAP. Especially on those SMR drives

I did stumble accross Dolphins PDF. However the price is quite high for the guide. https://www.dolphindatalab.com/product/wd-smr-scratched-hdd-data-recovery-solution/

If anyone can share the knowledge for the lower price. Please do. I am all ears. Many thanks!