It doesn't matter which soul is "active" because to both his souls, they are Yuno. The elf soul didn't control Yuno because it was Yuno
For example, Party and Vengeance are so different that they physically change appearance when they switch. Similarly, if Yuno souls would "switch," they are so much the same that it wouldn't make any difference physically or mentally. This means that it doesn't make any difference to the first grimoire who chose him but this also means that another grimoire can choose him because there's still another soul with no grimoire within him.
Think Asta's True Devil Union, Yuno's souls are like in True Soul Union or something.
Elf Yuno doesn't hate humans because he died in the womb, had no memories and thus no hate towards humans to be carved into his soul like the other elves.
For example, Party and Vengeance are so different that they physically change appearance when they switch. Similarly, if Yuno souls would "switch," they are so much the same that it wouldn't make any difference physically or mentally. This means that it doesn't make any difference to the first grimoire who chose him but this also means that another grimoire can choose him because there's still another soul with no grimoire within him.
Think Asta's True Devil Union, Yuno's souls are like in True Soul Union or something.
Elf Yuno doesn't hate humans because he died in the womb, had no memories and thus no hate towards humans to be carved into his soul like the other elves.