When I do a barrel roll and place the template all the way to the front, can I then place the ship slightly past the template in the backwards direction? This would be a legal position had I placed the template more to the rear. Or do I commit to the range of the template once I pick up the ship?

As per the rulebook:

Place one end of the template against either the left or right side of his ship’s base. (The template may be placed anywhere along the side of the ship’s base as long as no part of the template goes beyond the front or back edge of the base.)

If you look at example on page 8, position 2 could be the start position as well. It can go forward or backward of the template as long as you don't go beyond the template. This means you can extend forward of your current position, or rearward. This can be really helpful if you need to get a little closer to, or further from the enemy.

When you declare a barrel roll, you only need to declare left or right. You don't need to declare if you're placing it to the front or the rear of the ship's side. You are only committed to it if it will fit without overlapping a ship or obstacle, and that's only if you are playing the tournament rules. Under the standard rules, you aren't committed to anything.

So I should be able to put the ship back in the original position and slide the template back a bit if I do want to place it beyond the template?

On a similar note, would it be legal to use two side by side 1 forward templates to get the full range of barrel rolls on one side?

When you barrel roll the possible end point will fit into a pretty large rectangle. The furthest forward you could be is by putting the template and the front of your starting point and then putting it at the back of the ship's ending point. From there you can just slide ship and template back until the template is at the back of the starting position and the front of the final position.

In theory you could take two ships starting in the exact same position and roll them the same direction leaving them lined up. The only problem here may be the numbs might rub.

I understand how barrel rolls work. I guess my question is whether once you pick up the ship are you committed to the template placement or can you adjust it. That's either by replacing the ship in the original position and moving the template again or going against the rules and sliding beyond the edge of the template in the direction where you could have placed the template originally.

My guess is that casually people might be OK with it but I'm not sure about a tournament setting.

In a tournament you only have to declare which side. After that you can slide the template back and forth as much as you like. Merely placing the template doesn't commit it positioning, but it should give you a fair idea of where the ship is going to end up. There shouldn't be much need to go back to the starting point. Of course you can't go checking anything else (like ranges) and then move the ship back to its original point and start again.

I've always wondered about this, and at some point I decided it's just something I feel comfortable doing as a time-saving measure, as long as I know the final position is legal.