‘ Then Gideon built an altar there to Yahweh, and called it Yahweh-shalom. To this day it is yet in Ophrah of the Abiezrites.'
In gratitude Gideon built an altar to Yahweh, calling it ‘Yahweh is peace (or ‘well-being')'. This is a summary description of what follows so that this altar is the one he built on the rock in Judges 6:26. The use of such a pre-summary is a regular device in the Pentateuch. Judges 6:26 demonstrates that temporary altars to Yahweh could be set up for the purposes of sacrifice wherever Yahweh specifically commanded them (see Exodus 20:24-25). It may thus be seen as confirming that there was one central sanctuary but that temporary altars could be set up for a temporary purpose when specifically directed, and only then, by Yahweh. The sacrifices would be offered by a tribal priest, that is, one dwelling among them.
Alternately this may suggest that Deuteronomy 12:14 speaks of a central altar for each tribe (translating ‘in each one of your tribes') in the place where God chose, as well as one at the central sanctuary. But in view of Joshua 22:10-34 that is unlikely to be true at this time.