Mixing developers to get correct strength

Hi there :) I just have a quick question.
Can you mix developers with different peroxide amounts (but same brand & product line) to get the correct strength?

Just to expand, I ordered a bottle of osmo ikon cream activator 3% but received the tone-on-tone enhancer (almost 0%). They won't send the correct one until receiving the wrong one, and at this point I'd rather order a bottle of 6% and mix it 50/50. Sounds weird but it would actually be more cost and time effective with the options I have.