Of course they didn't give them permission to adapt the liturgy in an "illicit manner" because that would be a contradiction in terms, since what they specified would from then on be de facto "licit" rather than "illicit." But they clearly gave them permission to adapt the Mass in all kinds of various ways. These quotations give the local bishops and/or bishops' conferences permission to:
1. Encourage "participation" of all sorts with no limits specified. This is basically carte blanche to do anything they want at Mass.
2. Make their own decision on the vernacular, left up to the bishops' conferences. So again these decisions are left to their judgement and initiative. And even worse, the fact that the decision is made by a conference and not by an individual bishop means the bureaucrats are in charge. There is no way you can deny that this has been the reality since Vatican II. Nor is it a mystery how it happened.
3. To "inculturate" the Mass. This means that each region can decide what parts of the local culture are not in contradiction to the faith. So if the American bishops decide that our local culture is Elvis Presley, and they decide that Elvis Presley is perfectly consistent with the new concept of the post Vatican II Mass, then they can have an "Elvis Mass." Same concept with every other area of the world.