I use myself both GU10 and MR16 bi-pin (low voltage) LED replacements for what should be Halogen bulbs.
If you need the amount of light that you get now from the 50W bulbs, then no. This will not cut it.
But do you?
I have 6 GU10, 3W each LED that go on a fixture designed for 6 35W Halogen. For dinner, that is all I need. Yes, it is on the romantic side, but since you have 6, you can point 3 at the table and 3 at the walls around and you have both decent task light and ambient light.
Add to that the fact that there is the option (almost always)to add more ambient light (add the 3 LED above the bar next to the dining table, or the 2 wall lights in the hall next to it) and you are just fine.
In my kitchen, I have 12W LED recessed lights which replace 65W equivalent and they give PLENTY of light. you can do brain surgery under that light... So really, people give LED bad rap. They do great job if you get the right light for the right setting and make sure to get the right amount of Lumens.
The W per Lumen ratio is great, and light quality is great. It only fails when people don't realize that the things they buy, even though it should be clear based on the data on the package, are too weak to replace the incandescent bulb. a 3W LED cannot replace a 50W Halogen is the short answer, but LED CAN replace Halogen if you plan it right.
AFAIK, bulbs with a GU-10 base are driven directly from electrical mains, in which case it's OK to use a lower-power bulb. Your fixture won't reach the temperatures that it's capable of withstanding.
The only place that I know of that it might not be OK is with low-voltage (usually 12V or 24V) lighting systems such as track or task lighting: some transformers have a minimum power output that they like to supply, so if you use lower wattage bulbs, you should use more of them to compensate (somewhat defeating the purpose). If this applies, you would have an entry for Minimum power on the specifications for the lighting system.
Best Answer
Probably, but you don't want to.
As comments mention, there are several factors which play into the maximum wattage. You don't know which factor(s) was/were the driving factor(s) in that rating so you have no guarantee.
The consequences of ignoring it could be as benign as a fuse breaking, or as bad as the insulation cooking and releasing toxic chemicals which cause health effects, or just getting it done with and burning down your house.
Buying the right bulb is probably a lot cheaper.