Changing one part at a time is fine until you have forty to change. Select the rows and act on all of them together.
Every configurable table has a checkbox on each row and a select-all checkbox in the header. Mark the rows you want — or narrow the table with a filter and select everything that matches — then choose an action. The selection is kept as you search and filter, so you can gather a set across several searches before you act.
What you can do depends on the table. On most tables you can tag and untag the selection in one step, and set, rename, or delete a custom field across every selected record. Parts add more: add the selection to a project, to a meta-part, or to a purchase list; set low-stock levels or part attrition; archive or delete; or download the selection as a CSV.
Bulk custom-field editing covers the most common case. Set a manufacturer lead time on eighty parts, rename a field across a project's BOM, or clear a value you no longer track — one operation instead of eighty.
Physical inventory work is bulk work too. Select lots and move them all to a new storage location — moving less than a full lot splits it, keeping traceability — or adjust their counts to match a physical count. On plans without lot control, the same move and adjust operations work on the stock batches inside a storage location, so a shelf recount is one selection and one action.
Bulk operations are in every plan, including the free Maker plan.