Type of glue for sealing cable entries
Not what you are describing, but "duct seal" is a (all I've ever seen is gray) non-hardening putty intended for plugging conduits to prevent various things (air, water, rodents, insects) from coming along with the wires, usually at building penetration points. Find it where electrical supplies are sold, though it may not be all that obvious on the shelf.

It is removable and reusable.

What you are describing sounds more like hot glue (which could work, though its performance exposed to sunlight may be dubious.)