Welcome to the Forum,

You can using the Graphics tools — but why? 6/8 written as 2/4 goes back a few hundred years and is a staple of the March just as 12/8 written as 4/4 is a staple of Jazz. You would display 2/4 but write in 6/8. If some measures are actually 2/4, you would change it in the same dialog window. To keep the pulse steady, you would adjust the Tempo in MIDI, Expressions or Playback Controls.

https://usermanuals.finalemusic.com/FinaleMac/Content/Finale/db-time-signature.htm?Highlight=display%20different%20time%20signature 

This isn't the only way to do it. Most arrangements of "Jesu, Joy of Man's Desiring" give an indication of the eighth notes in the first measure, then handle the straight eighths without any marking. No one gets confused by this in the 400 years since written.

You can upload screen shots in jpeg and png (but not pdf). I've taken the liberty of posting yours. Anyway, the reason it's not used is because it isn't necessary.

Hi!

Thank you for your help!

To answer your question why? its because I am transcribing the example above and I am trying to do exactly the same as the score for the individual parts. And so, just to make sure I am clear, I am trying to write as exactly above 2/4=6/8 within the time signature, not to do it hidden which is easy to do.

Make your own.

Of course this is only for show. I used the Expressions tool. Pretty simple but if you want playback correctly you will have to use the normal Time Sig tool. Make sure you select Always Hide.

When you do your score simply copy and paste "the time sig" you created as you need it. Perhaps a tedious way but a way nevertheless.

What you want is not used in Western music—even if some engraver long ago laid it out that way. As I mentioned in my earlier reply, Finale has Graphics tools that let you draw anything you want as Ernest showed you. You will use the Time Signature tool to hide the real time signatures.

If you are making a performing edition, you can also do it correctly and paste a graphic showing the original time signature that you posted. That's another engraving practice that goes back a few centuries. 

Thank you!

I was complex to learn to use the shape designer, but I am pretty happy with the result.

Does that mean you are done and successful? I agree with Mike even if I were retranscribing it I would probably not use the = sign.