Although I have sympathy for your predicament, who is going to keep these paths open. This is the time of year when undergrowth is most rampant, in the days when footpaths were used for folks' day to day travel, the odd farm worker may have traveled them with a brushing hook, but the walker with such an implement on a public right of way will be committing an offence, and risking several years in prison.
Strimmers might be the answer, but the outdoor industry is yet to invent a light portable strimmer for the replacement of the machete to aid passage in heavy undergrowth.
Course on of the current trends in 'landowner' protest to enhance their attitude towards leisure walking is the fencing in or is fencing out of the actual right of way from the land it is associated with. This will cut it off from the normal field maintainance which will control weeds and heavier undergrowth. If change of management on a landowners land makes the right of way impassable then I believe it should be the responsibility of the landowner to make it passable, because he is effectively obstructing the right of way.
If landowners were more pro access then then there might be a more willing understanding for the rest of the community to join Parish Partnerships and keep parts of the social infrastructure clear, that get clogged by seasonal growth. Visitors bring income to those parts of the rural community they are attracted to.
In the past this time of the year is the time I choose to head for the hills, as the seasonal weed growth dies back I tend to do my lowland exploring.
If I were really young, fit and public spirited I suppose might be walking the countryside with a knapsack sprayer and double sided spray bar soaking the verges with 2,4D and other choice exfoliants to do the jobs that many of the country dwellers did 60-70 years ago manually and quite willingly, in the little leisure time their working hours allowed.