I'm sure Toady intends to clean up all the cumbersome interface things in the future. I'm making this suggestion on the off chance that it can be quickly/simply implemented as a placeholder because there's a similar option already present (and I don't think it's been suggested yet).
The title probably sums it up for most. All workshops that can decorate (metalsmith's forge, clothier's workshop etc) are given a new option like "Decorate flagged item/s" similar to the ""Melt a metal object" of a Smelter which only melts items that you have first marked for melting. Flagging an item for decoration can be done via the same steps used to mark something for melting. The current broad decoration options would remain for when you want to just decorate everything without marking it first (like when you want to decorate all your pigtail bags with rope reed cloth or whatever).
Extra stuff:
If we want to get fancy, and I hope Toady eventually does, the "Decorate specified item" option would branch out into further options depending on the workshop. So for example you flagged an -iron breastplate- for decoration and chose the "Decorate flagged item/s" option in a metalsmith's forge. The following options could then appear:
"Decorate flagged item/s randomly"
"Decorate flagged item/s with spikes"
"Decorate flagged item/s with studs"
"Decorate flagged item/s with hanging rings"
"Decorate flagged item/s with image" (waves, thick crosses, blazing suns etc)
"Decorate flagged item/s with creature" (dog, cow, minotaur etc)
"Decorate flagged item/s with historical image" (this relates to the taming of x by y, this relates to the appointment of x to the position of y etc)
"Decorate flagged item/s with image of an individual dwarf" (you want to stick an image of your current fortress queen on the breastplates of all the royal guard etc)
So you choose to decorate your -iron breastplate- with spikes. It then allows you to choose a specific metal from your available stock or a random metal option for when you don't care for specifics.