Charging a lithium-ion battery with 5V but stopping at 4.2V
Yes, you can do this, use a proper resistor, and then watch your DMM readings until it gets to 4.2 (or 4.35) V. But you need to be really patient, and better use a flame-retardant surroundings... The problem is in your possible lapse of attention since it will likely take several hours, depending on cell capacity and elected charge current. Li-Ion dedicated chargers do it for you automatically and more reliably.