Geared...I'd avoid.

I imagine that if you use 7 speed Powerlinks, you could add in 10 speed links as long as they're both "inner" links at the two ends.

I suspect it'll be acceptable as a short term solution on a bike that doesn't get much abuse, but I'd not be leaving it like that.

The amount of 10 speed Shimano chains I've snapped shortly after bodging them with a pin tool instead of a new pin or a quick link is, well... it's two. But that's enough to suggest an unholy mix of knackered 7 speed and much narrower 10 speed is going to result in a knee/stem interface as soon as you start pedalling up the nearest hill.

Otherwise, iirc the space between the inner plates on a 10 speed chain is also narrower so if you used a few bits of 10speed to lengthen the chain, you might find that the 10speed bit jumps on the smaller sprockets under heavy load as it doesn't sit all the way into the teeth as well.

Finally i don't have great experience of rejoining 'geared' chains for derailleur systems (ie ones that aren't bmx chains with massive outer plates and wide pins) without using proper joining pins or quicklinks/powerlinks; they tend to fail after a while at the point you pushed the pin back into the outer plate. Fine to get you home if you break a chain, but will break again later on at most inconvenient moment.

It passed the cycle stand spin the drivechain test.

But, will it work going up a hill with load applied?

It was "fixed" under duress, and my work was not guaranteed. Apparently the spare 7spd links were left on a window sill somewhere.

Shonkyness sprungs to mind!