Ballast upgrade from MH to switchable MH/HPS. Is it possible?

I have a Diamond 400W MH set-up (magnetic ballast) that was a cheap craigslist find. It came with an MH bulb and an HPS conversion bulb. I was wondering if it would be possible to convert it to a switchable MH/HPS ballast by wiring in an HPS igniter and a switch. Has anyone done this before? Would it be safe/worthwile? Unless I'm missing something, the igniter seems to be the only difference between the HPS & MH ballasts right? I found an HPS igniter on 1000bulbs.com for like 15 bucks; and seeing as the HPS retro bulbs are around $120 vs $20 (thank you Lowes) for a standard HPS bulb, it would be awesome if this upgrade were possible.

Yes you can and they even have HPS/MH bulbs that do all the work with one bulb to where you need no switchable ballast.