HM3 will not list all available popups as an option to use on any/every HUD like HM2 did. You have to open the HUD - HUD Editor and choose the 'Profile:' that has the popups you want to use on another HUD then click the 'Popup Groups' in the upper right corner. Choose the popup you want to export from the 'Group' list window on the left then click the 'disk' icon/button to the right of the 'Delete' button and export the popup/group. Then you change the 'Profile:' and repeat the process to import that popup/group to the other profile.
Here is a short video example of how to do those steps.
You can Ctrl+A or Shift+Click to select all/multiple stats before making the item property edits. HUD - HUD Editor - Ctrl + Left-Click multiple stats (or Ctrl+A for all) in the 'Group Items' list then make your edits to the item Properties - various fields that you want to edit for multiple stats at the same time. You can also select the 'Font' Item Property to select it then click Ctrl+C and go to the other Stat(s) and select their 'Font' then click Ctrl+V.