I assume that it is true that by working out your muscles, you gain strength and muscle mass. So, I also assumed that by going nuts on areas like the thighs & arms, you would see more muscle begin to form and could even increase the size of these muscles. I see female body builders whose bodies look like men! These masculine looking women aren't myths like the Lock ness Monster.
An increase in size, to an appreciatable extent, will only comes with correct training and calorie intake. However, most woman can NOT become to "look like men". Without the use of anabolic steroids. Hormonally, woman are not equip to grow loads of LBM.
Working out "specific muscles" comes down to goals. If weight loss/muscle preservation is key. Then the focus should remain on "big muscles". In terms of calorie expenditure, a bicep curl or tricep extension is useless.
Focusing in on "small muscle groups" is usually the goal for Body builders that are lagging in a specific area.
That all said, woman can NOT become "like men", as you said, without steroids. No matter the training or diet or time training.
So, not wanting to train the "big muscles" hard. Because of this worry about becoming "big" over night. Is flawed and a myth..