Mixing Formula

I was transitioning my son to a hypoallergenic formula so during the transition I mixed Gerber Gentle and Gerber HA. He's been exclusively on HA for a month but has recently been refusing bottles. He has also been on purees for a month now. His daycare teacher suggested maybe mixing formulas again, that he may not like the taste of the HA and is only drinking it when desperate. It's a struggle to get 28 ounces In him in a day. He's 5.5 months. Is it ok to mix formulas permanently?

Also, when we were mixing formulas I would proportion them everyday. Would it be out of the question to mix them together in one container and scoop out of that? They're both Gerber products.