Hi @bh99 ,
I wouldn’t risk it.
The lamp has been selected to work at the temperatures that may be present in the microwave.
Also using a higher wattage globe means that more current is needed and this may cause problems with the lamp’s power supply circuit on the control board if it has been designed for a 25W bulb e.g. lamp relay contacts may have a maximum current rating limit below the current required for a 50W bulb. I don’t know if this is applicable in your model but you would need the wiring diagram to find out if there is a relay or if it is powered some other way. Again it’s a risk which may end up with no lamp working at all.
The lamp is available from here at a cheaper price. Just search for LG 383EW1A077D to find other suppliers that suit you best. Your model is a rebadged LG microwave (or a made to order for Kenmore by LG) as all the parts in it are made by LG.
Also the lamp is a halogen type so make sure that you handle it using gloves because when you touch a Halogen light bulb with your fingers, you leave behind a residue on it which can in time cause the bulb to heat up unevenly, and even cause the bulb to shatter as a result.