well, at least for me it won't break too much. Because you won't design a rocket can barely lift itself, so maybe you will use more fuel to escape the atmosphere, but it will fly anyway.
Besides, all existing design is using stock parts so you won't get a lowered TWR and DV, and the design designed with upgrade can tell what upgrade is required to work, just as a part need to be unlocked before you can use that design. You won't call "broken design" if it requires ASAS and you didn't research it yet, right?