There's nothing wrong with using a block or piece of wood to hold up the arm, but for me is unnecessary. I am a top feeder. I have no reason to hold the arm up mechanically to change a blade or to feed it into the next hole.
To change a blade I just feed the blade through the fret hole, then the table hole, then mount it to the top blade clamp. Then mount the blade to the bottom clamp and tension. No need to raise the arm.
To change to another fret hole, release the tension, release the bottom blade clamp. With one hand raise the upper arm, move the blank into position, let gravity lower the upper arm while guiding the blade into the hole with the other hand. Then tighten the blade clamp and add tension. It take longer to explain it than to actually do it!
This process work well for most fret work but may not work well when using spiral blades with very tiny holes.