I need to replace some components contained in lots of our BOMS (500+). The revision will remain the same, we just want to replace an inventory item with a non-inventory item. I have uploaded BOM revisions before, but I'm wondering if there's a way to do a csv import to just replace one item, as opposed to exporting ALL components in a revision and uploading them all with the replacement item? Seem like you can either overwrite sublists or not, one way replaces everything and one way just appends the new item.

I don't think there is

Confirmed, there isn't. Bummer.

I have recently done the exact same exercise. I used a product called cloudextend for netsuite which allows you to edit Netsuite data in Excel. you can download the bom. use excel formulas to modify just the one component.