'Replace variable text codes in this custom content with these variables.'
Doesn't work as described for Custom Content unfortunately.
Created item with float item variable with selected data 'action', variable key 'ItemValue', LOCAL and then random number between 0,2 to 0,5. Then custom content of the item with key ItemValue with Default content 'var.cfloat=ItemValue#0.00'. After that, set up in Menu Screen Additional Content Layout with ID Item Value and Default content is 'customcontent=ItemValue'. It only generates one random variable at the first addition to the inventory and that never changes.
Since there is the same option for Description, took my time to test it. I've copied the same default content from ItemValue into Description and set another content layout underneath it. And that works fine. Use In Description works fine as I'm using both things at the same time and can see which one works.
https://ibb.co/7JswFs7 See link, below price is description field and the upper is custom content ItemValue. Both have enabled use of item variables and use same default content 'var.cfloat=ItemValue#0.00'.