Learn English – term that means temporary base camp

To borrow from programming terminology, to coerce or to cast might fit.

We can coerce an adjective into a noun by adding a -ness ending to it, which may be understood even if, technically, it isn't the correct noun form.

We cast expressions into variables to save our hands when writing equations.

Or simply even convert

We convert the function into this particular form so that we can make statements we already know.

The process of joining groups of humans and things are fairly distinct and probably call for different terms.

For humans, the verb substitute, or sub for short, may suit. The Macmillan Dictionary defines it as

[INTRANSITIVE] to do someone else's job for a short period of time; substitute for: Mark will substitute for me tomorrow.

For objects, the verb tack may be suitable. According to Collins, it means

to attach temporarily, as by sewing with long stitches

This can be applied to other materials, including metals, although some tacking processes (such as spot welding) may require a good bit of effort to reverse.