This is the second new topic of today and I am topic-ed out and thinking-about related matters-out. This will be the barest beginning of what I hope will become at least my record of experiences and maybe others will try.
1. You cannot succeed in the way that I began to see, with Long Form Viili. You need Short Form Viili.
Long Form viili will combine with kefir and you will taste both but the ropey viili ruins any chance of thickening in a way that is appetizing. I think vast numbers of people wouldn't know there is something better who have tried combining the two cultures. Yes, kefir can be thickened but you'd like it better using a custardy non-distracting type of viili instead of a take center stage easily-gain-attention type of viili, the long form.
When I combined the viili in the custardy form it worked to initially create a thicker lemony tasting kefir. My custardy form eventually transformed to what it remains, no going back now, Long Form viili.
That's what I ordered from an Australian ebay supplier. We thought I'd been sent the wrong culture! But no... I had the long form it took a while to develop. I do have yemoos LF viili in the freezer pending move.
Smearing the jar with the culture may have been a factor in the viili form change instead of merely adding it to milk giving it a stir and letting it sit.
The passage of time in the state of Hawai'i with maybe unique character might have played a role.
2. Mixing can be done as Nathan suggests in a thread on thickening kefir, in the first of two such thickening threads I think.
Thickening is achieved. The results are not merely viili with no kefir because even though viili is the faster set up there are ways to compensate.
3. From here on the sequence of events using viili in its evolving form from Short to Long because either way we are looking at, for a start
whether it can be done,
whether it damage or changes kefir grains,
how the results differ in several different scenarios, and
whether or not kefir-villi can take a second ferment with another food such as raisins, which I tried.