So if I wanted to select 20 weapons and change their ammo type in one sweep, is this possible? Using the picklists provided under search/replace I can find the ammo type of the selected weapons (say, 556), but when I look to replace all of these with a LIST it's not available as an option ... ? Is there no way to replace an ammo type with a list under search/replace?

Use NVEdit for batch edits, it's a lot easier- set the list on one in the geck & copy it across to the others in NVEdit.

I'm not sure what you just said (having never done this), but good to know it's feasible! I'll look into NVEdit tonight.

Out of curiosity,is it also a good tool if I have 170 items to merge into a mod? I typically use TESSnip, but the problem is copying each individually and then removing the duplicate ... do this 170 times and I start making mistakes [getting grouchy!]

Is there a tool I can use to copy across x-amount of updated records to copy across/and replace in another .esm/.esp? Same NVEdit?

Yep, those are the kind of things it's designed for.

NVEdit ROCKS - thanks for the recommendation!

Apologies for the noobness, but how do I copy a mass of items from one mod to another, overwriting the destination? I tried deep copy into and ctrl+c etc, but they didn't actually copy anything across; is there a trick to it?