Is there an easy way to remove and replace the front differential in a 2003 Chevy Trailblazer without having oil pan?

No, there's no easy way to remove and replace the front differential of a 2003 Chevy Trailblazer without removing the oil pan. The oil pan (or at least the lower part of the oil pan) is very likely in the way of lowering the differential. Even if you could *maneuver* the differential out without directly hitting the oil pan, the proximity and risk of damage makes it extremely impractical and risky.

The front differential is a relatively low-hanging component, and the oil pan's location under the engine makes it a necessary part of the removal process for nearly all vehicles, including your Trailblazer. Attempting it without proper removal of the oil pan (and potentially the drain plug) severely increases the risk of oil spills and damage to both the differential and the engine.

You'll need to properly drain the differential fluid, disconnect various components (axles, driveshafts, etc.), and likely drop the oil pan or at least lower it significantly to gain sufficient clearance for the differential to come out. A service manual will provide detailed instructions and diagrams.