You never WANT to walk on any roof, ever. I had a leak free roof that cracked with each footprint and in weeks I had to redo the entire roof and repair the water damage inside.
Anything you can do from the ladders on the side is best. I use plywood to spread out my weight and lie down for repairs. Eternabond Tape is great for sealing all vents and such.
It's a one sided tape you apply with pressure for a permanent seal. And I use Eterna-clean as well for surface prep. But be aware. One you set this tape down, it can NOT be repositioned.
I use the white version for aesthetic reasons. Its pricey, but permanent. I have managed, with much effort, to roll the tape into tubes and use it as a window seal instead of caulking.