I want to use CSV import to update product TAGS in bulk for many of my products, but don't need to change or update any of the variants.
If I remove all rows for variants, just leaving the main product row containing the TAGS, will this in any way affect the product variants?
Also, what columns do I need at a minimum to do this? Do I need ALL the columns or just a required few (and which ones)?
I don't want to mess things up by not knowing how Shopify handles import of CSV files.
My thinking is the less the better for speed of import, etc., just keeping the minimum required structure for it to work correctly.
The key thing to remember is if you leave a column in your csv import (even if it is blank) then that data will be overwritten. So in your scenario you would need to make sure you remove the option columns as if you leave them in but remove the variant rows then the variants will be deleted leaving only a simple product with your new tags.
Try a test with one product and drop all your columns except handle and tags then remove variant rows.
If you can update them based on rules (example, update all tags for products in collection X), then you can use a free app called Bulk Edit Tags. Then you don't have to deal with the risks of CSV uploads.