There is a short answer to returning to the "classic" style UI in Dragonflight Pre-Patch: you can't return to a perfect version of the old UI that you were used to for so many years. While there is a dropdown under ESC > Edit Mode that allows you to choose between Modern and Classic, this does little to change the view other than moving the location of the player and target frames. It does not revert the UI back to the way it was.
Copy and paste this into the Import Text window:
0 30 0 0 0 7 7 UIParent -265.0 53.3 -1 ##$$%/&('%)$+# 0 1 0 3 5 MainMenuBar 4.0 0.0 -1 ##$$%/&('%(#,$ 0 2 0 7 1 MainMenuBar 1.7 4.0 -1 ##$$%/&('%(#,$ 0 3 1 5 5 UIParent -5.0 -77.0 -1 #$$$%/&('%(#,$ 0 4 1 2 0 MultiBarRight -5.0 0.0 -1 #$$$%/&('%(#,$ 0 5 0 7 1 MultiBarBottomLeft 2.3 4.0 -1 ##$$%/&('%(#,$ 0 6 1 1 7 MultiBar5 0.0 0.0 -1 ##$$%/&('%(#,$ 0 7 1 1 7 MultiBar6 0.0 0.0 -1 ##$$%/&('%(#,$ 0 10 0 7 1 MultiBarBottomRight -121.7 4.0 -1 ##$$&('% 0 11 0 7 1 MultiBar5 -356.6 4.0 -1 ##$$&('%,# 0 12 1 6 0 MainMenuBar 0.0 5.0 -1 ##$$&('% 1 -1 0 7 7 UIParent 31.7 258.0 -1 ##$$ 2 -1 1 2 2 UIParent 0.0 0.0 -1 ##$# 3 0 1 0 0 UIParent 4.0 -4.0 -1 $$3# 3 1 0 0 0 UIParent 268.3 -5.7 -1 %$3# 3 2 0 1 1 UIParent -461.4 -9.0 -1 %## 3 3 0 0 0 UIParent 19.7 -165.3 -1 '#(#)#-#.#/#1$3# 3 4 0 5 3 LootFrame -4.0 125.7 -1 ,#-#.#/#0#1#2( 3 5 1 5 5 UIParent 0.0 0.0 -1 &#*$3# 3 6 1 5 5 UIParent 0.0 0.0 -1 3# 4 -1 0 4 4 UIParent 298.3 -223.3 -1 # 5 -1 1 6 0 MainMenuBar 0.0 5.0 -1 # 6 0 1 2 0 MinimapCluster -10.0 -10.0 -1 ##$#%#&.(()(*# 6 1 1 2 8 BuffFrame -13.0 -15.0 -1 ##$#%#'+(()(*# 7 -1 1 6 0 MainMenuBar 0.0 5.0 -1 # 8 -1 1 6 6 UIParent 35.0 50.0 -1 #'$A%$&7 9 -1 0 7 1 MultiBar5 266.0 4.0 -1 # 10 -1 0 3 3 UIParent 167.7 209.0 -1 # 11 -1 1 8 8 UIParent -9.0 85.0 -1 # 12 -1 1 2 2 UIParent -110.0 -275.0 -1 #K
Some things worth noting:
The wyverns/gryphons on the ends of Action Bar 1 were removed with "Hide Bar Art" for a cleaner look and more space. However, the scroll bar on the end was maintained in case you want to keep that feature of a scrolling bar (I often put my profession links there personally). If you wish to remove the scroller, go into Edit Mode, right-click Action Bar 1, and select "Hide Bar Scrolling".
Action Bar 3 was programmed with the Control buttons like in the old UI. You can right-click Action Bar 3 and select the Quick Keybind Mode button (pictured above) to set them to your own keys.
Action Bars 4 and 5 default to the side position, which is why the bars appear a little out of order. 1, 2, and 3 are on the bottom, 4 and 5 are on the right side.
Action Bar 6 needs to be activated manually, either before or after you've imported the UI. It will slide into its proper place without any further intervention once turned on.
Tweaks and Modifications
On some characters, I like to have a short bar for such things as Aspects and Traps for hunters, or Totems for shaman. I usually handled these through addons, but these are not all working properly at present.
You can easily add a small bar with any number of spaces up to 12. This shows how I created my Aspect/Trap bar for my hunter, where I changed the number of icons to 7 (I don't keep some of them on my bar regularly):
WoWhead Article Link