I am working on a product that I don't feel is completely ready but I have a set of users that are very interested in using it now as "alpha" testers.  I would like to give them the product now for free as "alpha" testers, but I would like to later license the software.

Is this possible?  Can anyone point me to any links/books/articles/etc?

Thanks.

EDIT:  Due to the lack of my clarity and the reponses to the question I thought I should add this statement.

I haven't decided if I am going to close-source or open-source this project yet. The user base that wants to get their hands on it now has kind of surprised me and I was concerned about what my options are as far as being able to give it to them now as open-source and later change to closed-source, or even vice versa.

Thanks to everyone who has answered and commented.  I appreciate it the insights.

If you own all the code, then you can re-release it under whatever license you want. 

The problem comes if someone has contributed patches to the project. What usually happens is that they own that code, and they contributed it under the current software license. (You should have some sort of contributers agreement that covers this.) Therefore, to re-license it you will need their permission. Depending on how may contributers you have, this could be hard. For a reference for this, look at the OpenStreetMap license change and how long that is taking.

But IANAL, disclaimer etc.

And what people will make of your license change is another matter, as another answer comments on.

EDIT: I answered this as it relates to open source products. But re-reading the question I see it's not clear whether it's closed source or open. 

If you are talking about 2 closed source licenses it's easy: If you own all the code, then you can re-release it under whatever license you want. Just make your alpha version commercial closed source license, all the usual terms (no copying etc.), just with a price of zero. 
