minecraft-java-edition,minecraft-commands – How to Add Custom Head and Name on Mob with Command Block in Minecraft

When you place a named block, it loses its name tag, making it impossible to detect if it was ever named. What you can do, however, is set a custom data value:

/setblock ~ ~ ~ diamond_block 1

Then, replace detect ~ ~-1 ~ diamond_block 0 with diamond_block 1. You can use values 1 through 15, but values above 15 are not supported.

Note: In some versions of the game (and possibly the latest updates), blocks with custom data may have a missing texture, and the custom data may not be saved properly. You'll have to look into this yourself as I can't test it at the moment.

The NBT data for /clear (and /give and /replaceitem) is already starting within the tag compound of the item format, which will be compared to each of the player's slots automatically. Setting the Damage value to -1 allows finding any Damage value. The Damage value is also specified before the maximum number of items to remove, which you can also set to -1 to clear all items.

/clear <player> [id] [Damage] [maximum amount] {tag}
/clear @a[tag=!testtag] minecraft:leather_boots -1 -1 {display:{Name:"test"}}