You don't even need a special mode in the game. I think all you need are the OOTP equivalent of something commonly found in strategy games: difficulty settings.
Difficulty settings in OOTP would entail having a variety of options and settings bundled together that are turned on or off by selecting that difficulty level (if one finds the word "difficulty" problematic in this context, then substitute "complexity" instead).
The simplest setting, for example, might turn off just about all the transaction rules and related settings, meaning the GM doesn't have to worry about options, waivers, or any of that stuff. They can just concentrate on building the best roster for their team. Think
Front Page Sports: Baseball for an idea of the GM complexity involved.
The highest setting, which one might call the "hard-core" or "grognard" setting, would turn on every transaction rule and turn on all relevant game selections. The person playing this setting has to deal with every nuance and technicality of major league transaction rules, maybe even some they've not heard of before. (It's not called the grognard setting for nothing!
)
You could have any number of settings in-between these, catering to different levels of complexity.
The advantage is that the user can select their preferred level with just a single click, and thus don't have to hunt through a bunch of menu screens to find the game options they want to turn on or off—it's all been taken care of already. (And, of course, for the tweaker, they could select "custom" and then go through the menus turning on or off options individually as they please, just as is the case currently.)