Shopify native CSV import can’t do that.
If you open to using apps, Matrixify can do that.
Check similar topic – Inventory importing
Note that Renars is with Matrixify, just in case.
If Matrixify is too expensive, technically it’s possible to natively upload this “delta” into a metafield, then have a free Flow app to loop over those products and apply delta from metafield to inventory levels.
Would need someone to create a flow for your though.