My Blocks with return parameter
Can I only set an [out] param once?


Yes. You cannot tell it to be 2 different values at the same time. This applies to any block, not just the output block.


  Does setting the [out] param act like the "return" keyword?


Not really. The return keyword in most (if not all) programming languages causes the function to exit, which is not the case here. It just allows you to assign the output value (or values - you can have more than one output parameter).