OP CLI - Unable to build a list of item categories

For creating one item through piped input, like in your example, you could use op item template get LOGIN | op item create -. Alternatively you could save the output of the first command to a file and edit with the desired fields: op item template get LOGIN --out-file my1PasswordTemplate.json. After you have created multiple such files you can do something like find . -maxdepth 1 -name '*my1PasswordTemplate*' -exec awk 'FNR' {} + | op item create -. The first command searches all files with my1PasswordTemplate in their name and outputs their contents and then the pipe will pass these contents into the create command for creating multiple items.

Hope this helps a bit,
Andi