This sounds like you actually want to create an info record at a different organisation level along with entering price conditions at this new level + making the conditions invalid for the plant level. These are actually 3 different tasks (extending purchasing info record, creating price condition, updating price condition) from a program point of view.
You may be able to combine creation of purchasing organisation level and creating a price condition in one recording, but setting the price condition at plant level invalid would better be made with a separate recording (if recording is only choice).
With batch input method (and recording) it is not possible to create info records for a given vendor/material combination with different info record numbers, so you can just ignore the info record number field.