Is aluminium foil a good substitute for kapton tape when soldering?
If you are using a iron, then just apply it where needed.  Other nearby components won't that that hot unless you do something really wierd.

Also, Kapton tape doesn't protect against heat.  It keeps things from getting soldered by being a physical barrier to molten solder.  The reason Kapton is used instead of other tape is that Kapton can stand high temperatures.  It's also useful that solder doesn't wet Kapton.