Since Gelbooru has a close enough tagging system, would it be safe to copy and paste the tags from the same pic over at gelbooru and just delete the ones that's aliases to invalid and just have 1 post? I ask because I'm on mobile

Not directly, no. Some of their tags are used differently to ours so you'd still have to go through them.

BlueDingo said:
Not directly, no. Some of their tags are used differently to ours so you'd still have to go through them.

Thus me fixing what's necessary, which I implied in the OP

It's not just tags aliased to invalid_tag. Some tags there mean something else here and are under a different tag here. Those will need to be retyped.

Other than that, yes, you can copy them.