I checked it out and there is a way to do it but personally I would go for a mod or some perform logic as this is a bit cheesy, somewhat confusing and certainly time consuming.
Customizer is not conducive to the idea of multiple dialog boxes for a single line. But I'd also like to say the initial premise of having to fill out 50 UDFs on a single line, whether on the grid or in 4 dialog boxes is time consuming data entry to begin with. And S/O Entry overall may just run slower managing all these fields.
Here's what I mean by not conducive.
Let's say you want 12 of the 50 line UDFs on Dialog Box 1. Now let's say you created 12 header UDFs with the same name (or nearly the same name). Now you put those 12 on the dialog since they live on the header. Next to those, off to the right you insert a Customizer button tied to a script.
So the flow would go like this:
User is on Lines tab. They click their mouse on Line 1. Then click your button that pops the 1st dialog box of 12 UDFs. They fill in the UDFs and click the script button to the right. It sets the value of those 12 values into the line UDF equivalents (don't even need to add those lines UDFs to the grid).
Then they click the normal OK button on the dialog to close it (IOW 2 buttons to click in the dialog). The command to auto-click the normal OK button doesn't seem to work there. A workaround would be to have 12 event scripts (1 for each UDF) to replace the 1 button script).
Now that's done, the users clicks Dialog box 2 for the next 12 or 13 UDFs and repeats. When they're done with dialog 3 and 4, they have finished Line 1!
They move to the next line and press Dialog Box 1 again. The problem now is the values from Line 1 are still ""remembered"". We can't run a script when the dialog loads to clear them out so this becomes confusing.
And I think they'll feel like they're in button click hell (unless you have 1 crazy dialog of 50 UDFs). Have you thought about adding the line UDFs to the grid and using the wide panel? This is a case where having secondary grid off to the right might makes sense.