I basically did exactly this but was too slow about it, so I'm pretty sure it works.

The first part can be done much, much more easily with beempy's allow command. 

>allow -a targetaccount --permission active --weight 10 signingaccount

and then when you get to the last one  add --threshold 40 after the weight. (Don't do it before or you won't be able to add new ones without the owner key or building a multisig transaction to do it.)