What's the adjective for "by distance"?

If I had to describe a state that occurred only for a certain amount of time, I'd simply use the adjective "temporary" to describe the state (or the adverb "temporarily" to describe the verb). What word describes a change by distance (without regard to time)?

For example, if I were giving spoken driving directions that go through a road whose name changes from "Park Avenue" to "Main Street" and then back to "Park Avenue", I might say:

Park Avenue changes temporarily to Main Street.

I think most people would hear that and understand clearly what I meant. However, "temporary" refers only to time (not distance), which makes me question whether I'm correctly using the word. After all, Park Avenue at mile marker 50 is always Park Avenue. What's a more appropriate adverb to describe "changes" in this context?

You could use briefly:

Park Avenue changes briefly to Main Street.

Note that briefly is defined by Merriam-Webster's as:

1. a: in a brief way

…and, more usefully, brief is defined as:

1: short in duration, extent, or length

So the brevity of Main Street can be in the distance it covers.

This question contains a false premise. You assume that temporary refers in the example only to distance, and not time. This is incorrect.

When you give directions, you are creating a context, or background, to your statements. This context is the process of actually following (in your imagination) the driving directions. This is both a temporal and a spatial process, so it is perfectly natural to say, for example, "turn left at the light, go three blocks, and then it's on your right". Plainly the word "then" refers to the temporal order of events.

This is why "Park Avenue changes temporarily to Main Street" is also perfectly natural in the context you have created. The name of the street you are driving on does change temporarily, as you follow (in your imagination) the driving directions in their temporal order.

It is quite common to use becomes:

Within the town limits, it becomes West Main Street until it reaches the town center at its intersection with Pennsylvania Route 89, where it becomes East Main Street. Outside the town limits it becomes East Main Road until it reaches Pennsylvania's border with New York.

Some people also will use "turns into" in place of becomes.

Also note, that occasionally two roads of different names sometimes share the roadway for some distance and then split again. In this case one would say that one road joins or is joined with/by another for some distance.

I-70 is joined with US-24 from the Colorado state line until US-24 splits at Levant and runs north of I-70.

In your specific example briefly could be used (as Cameron suggests) as:

Park Avenue briefly becomes Main Street.