To the best of my knowledge, all software in this distribution is freely redistributable (libre, that is, not necessarily gratis), within the Free Software Foundation's definition and the Debian Free Software Guidelines. Where the two conflict, we generally follow the FSF. If you find any non-free files included, please contact me.
That said, MiKTeX has neither a single copyright holder nor a single license covering its entire contents, since it is a collection of many disparate packages. Therefore, you may copy, modify, and/or redistribute software from MiKTeX only if you comply with the requirements placed thereon by the owners of the respective packages.
To most easily learn these requirements, I suggest checking the MiKTeX package catalogue. Of course the legal statements within the packages themselves are the final authority.
In general, you may redistribute MiKTeX, with or without modification, for profit or not, according to the usual free software tenets. Here are some general guidelines for doing this:
If you make any changes to the MiKTeX distribution or any package it contains, besides complying with any licensing requirements, you must prominently mention such changes in your modified distribution so that users do not take your work for mine, and know to contact you, not me, in case of questions or problems. A new top-level README.yourwork file is a good place to describe the general situation.
Especially (but not necessarily) if changes or additions are made, I recommend a clearly different title, such as “Your work, based on MiKTeX x.y.zzzz”, where x.y.zzzz is the version of MiKTeX you are using. This credits both my work and yours.
You absolutely may not place your own copyright on_ th_e entire distribution, since it is not your work. Statements such as “all rights reserved” and “may not be reproduced” are especially reprehensible, since they are antithetical to the free software principles under which MiKTeX is produced.
You may use any cover or media label designs that you wish. Such packaging and marketing details are not covered by any MiKTeX license.
Finally, I make the following requests (not legal requirements):
a. Acknowledging that MiKTeX is developed as a joint effort by all TeX user groups, and encouraging the user/reader to join their user group of choice, as listed on the web page http://www.tug.org/usergroups.html.
b. Referencing the MiKTeX project page: https://miktex.org.
Such information may be placed on the label of your media, your cover, and/or in accompanying text (for instance, in the acknowledgements section of a book).
Finally, although it is certainly not a requirement, I'd like to invite any redistributors to make a donation to the project, whether cash or in-kind, for example via https://miktex.org/giveback. Thanks.
If you have any questions or comments, please contact me. In general, I appreciate being given the chance to review any MiKTeX-related material in advance of publication, simply to avoid mistakes. It is much better to correct text on a DVD label or in a book before thousands of copies are made!
I am also happy to keep anyone planning a publication informed as to my deadlines and progress. Just let me know. However, be aware that MiKTeX is produced entirely by volunteers, and no dates can be guaranteed.