Lmaoooo I don’t think Itachi would mind too much. As long as it was in the name of fun, and not entirely malicious. And not when he was working or busy. You can tell when Itachi has a lot on his plate. You can just feel the stress radiating off of him. It’s best not to try to and prank him at these times. He doesn’t find it amusing. He’ll glare, and that glare is scary

Luckily, Shisui is good about gauging Itachi’s demeanor. So he knows the right time for pranks. Shisui’s favorite prank by far was getting the s/o to subtly paint Itachi’s nails with one of those polishes that changes color in the sun while he was asleep. He goes to work the next morning with pink nails. 

This has to be executed with furtive talent though. Itachi is a light sleeper and wakes up fast. He’s a shinobi, after all. Shisui probably had to help the s/o, bc he’s sly and silent as a mouse

Sasuke pretends he doesn’t like pranking his brother but he enjoys it. Once the prank is done he starts blaming everyone else though. He swears that “I told ______ not to do it” or “I told Shisui it was a stupid idea” all while trying to hold back a smirk

Overall though, Itachi would appreciate a prankster s/o, but there’s a limit to how much he can take. Don’t make it an every day occurrence and certainly don’t do anything that could damage his reputation (the pink nails thing went a little too far. He was not happy about that) But he just makes it so easy. Shisui and the s/o think he needs to lighten up a little. That’s why the gotta prank him every now and then