Muto can be used to make permanent changes, just not the way you might expect. The easiest is changing the shape of something (Rock of Viscid Clay). However you can also do things like purifying/separating something by changing (part) of it. For example you can change impure silver to a liquid and skim the "slag" from it. It is also useful to blend/alloy solids by changing them to a liquid or gas for a short time.
As for changing sand into glass, that is straight ReTe Craft magic. Craft magic does not require requisites for intermediate stages. You see this in published spells for working glass and metal, which do not include Ig.
For light and heat, you need +1 Flexibility to do both. My group required +1 Complexity to match sunlight (for growing plants) with a "sun replacement" item, though this is YSMV.