Would it be possible to add the ability to /give blocks from this mod?

Idk what you mean. Can't the blocks be given from /give?

As far as I can see, no :( I can test again but yeah every time I've tried nothing comes up and I have to go into creative mode to get blocks

Seems strange. They should appear in command suggestions. Make sure the block or item ids begin with extshape:.

I don't know what i was doing before, but it seems to be working now. Looks like I might have needed to type in that extshape: at the start and I didn't know!