Q: How do you stop stock changes for selected items only?
A: Stock control is at an account level. You can turn off stock control by setting Auto Update Stock to No in your marketplace settings, but it would apply to all items in your account.
It would be more efficient to pause repricing on your items by putting a checkmark next to them and clicking Multi-Item Actions --> Pause Updates on Selected Items. However, please note that both price and stock changes would be stopped for those selected items.
The last option would be to run 2 separate Sku Grid accounts where one is set up with Auto Update Stock set to No and move the items to that account if you don't want their stock changed. All other items should remain in the original account and you should be cautious to never mix them between the two. If you're selling on eBay, whichever repricing method you're using, you'd need a separate instance of it for your 2nd account as well.