I think you can, but you need to ensure that at the relief flow rate you don't exceed the allowance on the inlet pressure losses (3% of set pressure from memory). If the inlet flange to you4 relief valve is a 1" connection, then 80mm extra 1" line shouldn't have a big impact, but you need to prove it. Only you have the knowledge about what this is protecting, how long the 3" line is from the pipe or vessel you're protecting and what the flow rate is.
Another time, might be better to post in the Chemical Engineers Safety relief valve forum.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.