Currently all they can do is import items from live for now as I dont think they've finished figuring out how to make the software work with mabi's client, and creating custom content like this likely would take a very large amount of time even when they get it working so I'm willing to bet that this kind of thing isn't something that will even be considered for a while.
We are able to make custom items, and we have quite a few of them in the game already.
I think here is a different idea of what is considered custom content. They have created custom items, but as far as I know the only ones currently released in game use existing models and meshes to create a new item from those pieces. By that definition we do in fact have quite a few custom items. However if we go by the definition of custom content where the item, model and meshes are all new to Mabinogi, I don't think we really have any of that. There may be some recently made that are infact completely new models thanks to the PMG Editor 2 that the dev team has. But most models currently in were made using the old pmg editor, which means they are mostly stitched together models from elsewhere. Take for example, the spear of ice. Its a trinity staff with the head removed, flipped upside-down and a ice pole shrunken down to use as the Spear tip. A custom item, but also not one making use of new, never before seen models.
Some things, like the dragon line of weapons, or the Silver Sword of the Shining Forest, were found items in the game files that were never used but brought to life by the team. At the moment with the existing old pmg editor available to the public making high quality models isn't really possible. They phase out when you get to close to the model, or have horrible texture stretching because the UVs didn't hold up through the file conversion to a PMG.
I'm hopeful that the new editor fixes the problem of the old one, and we can see proper models created custom for Mabipro imported into the game. At the moment, things like this https://www.youtube.com/watch?v=5oVPl2P3IN0
may look good but falls apart upon close scrutiny of the models quality.
Don't get into the Totemizer.