The only scopes you can adjust for parallax are, well, Adjustable Objective (AO) scopes. If your scope doesn't have an adjustable objective lens assembly, then it's fixed wherever the manufacturer decided.
Generally, if the parallax is set for 100 yards, it's okay for longer ranges. Problems can arise inside maybe fifty yards; certainly in the "up close and personal" distances inside forty yards. However, the small errors at such close range won't affect most hunting.
