One way to easily transfer labels from one board to another, is to create a dummy card, assign all available labels to it and then move it to the new board. In this way only the default unnamed labels have to be removed.
The filter is only applied for cards on that specific board, however if you have the same label applied across different boards you can use the search feature along with our search operator "label:" to search for cards across all boards with that label.
You can read more about all the search operators available here:
You can find cards without labels buy using the - operator. For example, if you have a label called red and a label called blue and you want to see all cards without a label, try this:
The result will be any card that does not have the red or blue label. Of course you will have to list all of your labels for this to work.
Both of the actions you described use the DELETE HTTP verb. Is your proxy blocking non-GET/POST/PUT requests?
Other things that use DELETE, for testing if this is in fact the root issue:
Removing a member from a card
Deleting a card
Removing a member from a board
Removing a vote from a card (requires the voting powerup to be enabled)
Just discovered the Chrome Extension Ultimello for Trello.
A big bonus is that it can do this in a UI only way so it won't save the order for everyone. You can also apply the sorting (it take a bit to do so).
Trello outlines their development thoughts of this as a feature here.
If you have Trello Gold, one workaround is to save a search with your specific criteria.
To find all of X label on Y board:
Then click "Save this search" in the search box. It's cludgy but it works. There might be a plugin/extension to do what you're wanting as well.
You can use the third-party automation tool Butler for Trello to do the job for you.
Log on to the Butler for Trello dashboard
Invite Butler to your Board
Click Edit Board to create a command
Use the Triggers and Actions panel to enter your command
when a card is added to list "B", remove all the labels from the card, and add the "Specific" label to the ...
Click on any card
Click labels to view existing labels
Next to each label is a pencil icon you can use to edit the name and colour of the label. Click it.
Click the delete button. This removes all instances of the label so be sure to filter for that label first.
There's no way to do it (https://webapps.stackexchange.com/a/43602/118250)
Alternating between the < or > key and the left or right arrow keys can be pretty quick to move from one list to the next, though hundreds would still take a while.
The fastest way to do it if you want to remove a lot of labels:
Position the cursor over the card and then press l and then the number of the label. You find the number of the label when you open a card and press on the label field.
Archiving a label will allow one to delete the item.
Mouse over the label.
Click the pencil icon, or click the label > then click the "Archive".
In the right "Menu" area at the top click "More..." > then click "Archived Items."