First of all, i assume you have already saved your .mc6 file (in the material tab, click on the + in the library, you'll have to choose if you want to save as a single material, or a collection). You can have a general view of all Poser file extensions at

All you will need is... a text editor! (simple, isn't it?).

Make sure you make a backup of your .mc6 file!

Then open it with your text editor. You'll have this:

The trick now is very very simple. You only have to change the words "mtlCollection" into "figure":

Then, you save (not save as, only save, that's why i asked you to make a backup). Now, you only have to change the .mc6 extension of your file into .pz2 extension, and to put it into your Pose folder. That's all!!!