Is there a soft ware that enables a user to edit(MOD) a game, particularly the classic R.T.S Command and Conquer Red Alert 2:Yuri's Revenge?

Everyone knows that IT IS POSSIBLE, I have seen, downloaded and used some MODS that were created by others -who prefers themselves to be called MODDERS(came from the word MODIFICATION and MAKERS: 'MOD' 'ERS' with the addition of one 'D' = MODDERS).

I recently read an article on E-How's website and discovered that each game has its own EDITOR that will enable a user to modify the RULES, GAME PLAY and 'REDESIGN' the game's units. HOWEVER, the name of the soft ware was not supplied, and I'm having a hard time browsing Google -for it only returns vague results.

Can you help me out? I would really like to create my own MOD(MODIFICATION) to Command and Conquer Red Alert 2:Yuri's Revenge so badly.

Can someone please tell me if you know:

1. any website(direct links preferred, IF POSSIBLE ;)) that contains some USEFUL information on how to get started on MODDING?

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2. do you know(by chance) any soft wares that can EDIT the RULES, GAME PLAY and 'REDESIGN' the game's units?

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3. I have this idea of mine that using photo-editing soft wares(Photoshop, GIMP, MS Paint) might help me modify the appearance of the game's units. Is this possible?

P.S. Sorry for this, but if someone will just reply with "WHAT?, ?!, HUHH?" or any other more, please include your reason for replying like that, like this:

"WHAT? What are you trying to say? Mind explaining more?"

... or something like that. I just really want clear, definitive answers that can help me, and not by answering my question with another question.

:::-Any efforts to answer my question will be much appreciated!-:::

:::-If you would like to mail me about my question, just mention it with your answer.-:::

Thank you guys for reading(and I hope leaving with answers)! :DD