It depends.
How old is this unit.
Be aware some drivers may just not work depending what it is.
I had an old del with 2gb ram I was able to update from 7 to win10, but it was a joke, worse after bits died and got fixed I was never able to load or activate any windows os on it and had to bin it.
I have also had units which while they can run windows are just not able to do anything else.
Some hp units depending on age have driver issues.
So simple point, yes, the accessibility upgrade for 10 can still be installed.
Weather you will be able to get it installed or even if it passes checking by the upgrader if you will be able to get trouble free work from it is another matter.
And it may not qualify for anything over a certain update.
I suspect that eventually older units will not be able to upgrade at all.
In the first release of 10 ms pushed it out to as many as they could.
Aniversary had a little harder requirements for hardware creaters will have harder requirements.
I am not sure but as I say it all depends on things.
For myself I am happy with 7 for how ever long it may last here.