Importing a blueprint from another faction is not going to work, for any faction. This is because all factions, even moded ones, have their own block IDs. All the block in Reassembler, even though they have the same shape and characteristic of other factions block, they do not have the same block IDs...

I see, is there no way around this ? Generally this makes sense, but for your Mod it would indeed make sense being able to use all blueprints

To have a faction with all the blocks, like Reassembler, as a mod, there is no other way than duplicating each original factions blocks to new IDs. Before the Steam Workshop integration, the only way to have all blocks was to directly edit your save game and specifically setting all blocks as unlocked...

I know this can get confusing. You have to consider Reassembler blocks as "original" ones. But they are, indeed, copies of all other factions blocks parameters. The cores are completely original however and not copied from any factions.

You could use the "console" or the "sandbox" mode to open another faction blueprint, spawn all Reassembler blocks and rebuild, piece by piece, the design. Not actually easy to do as there is a learning curve associated with using the "console" commands and this is somewhat outside of a normal game progression, but this is feasible.

It would make sense to take this into dialog with the Game Developer, he may cnosider a sollution for it - expecially now while Workshop support requires more flexibility.