I don't think a written permission is needed to fork, but it should meet declared conditions.
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As I mentioned in my original comment it is somewhat debatable whether this applies to hard or soft forks that may be adopted by witnesses, but it became an issue in the past when some independent developers were unwilling to release an alternate version for witnesses voting because it could potentially violate the license. At a minimum some clarification is needed (ideally in the license text itself).
This reasonably clearly prohibits forking the software to "use" with an entirely different blockchain fork as is common for other free open source blockchain projects. Repeating what I said wrote above, the practical advantages or disadvantages of this are debatable and widely debated, but it still contradicts the generally accepted notion of free (freedom) software.
Right. Saying "free" can be misled since it means "free under following rules".