The reeds are nominally within their limits once the lamp is running but, depending on which sort of Xenon lamp it is, inrush current could give them a nasty fright. For long lifetime I'd add some sort of buffer - see below.
You say "Xenon light bulbs". This might mean
Which it is affects the answer.
A Xenon filled filament lamp will have substantial inrush current which means a different solution is probably needed.
A Xenon HID lamp will have a controller. Some of these offer zero inrush current. Others may have an inrush type effecyt, although the mechanaism is differnt to that which applies in a filament lamp.
Maximum brightness possible will probably be achieved by using LED bulbs.
The best of these offer much more light than even the best halogen-xenon filament lamps.
HID Xenon lamps are closer to LEDs in efficiency but a good LED lamp is still better.
Current for a 12V at 5 Watt load is notionally given by
I = Power / Voltage
= 5W / 12V ~= 0.42A
so a 0.5A switch is notionally just within its rating.
In practice it will probably have a short life.
DC switch current ratings are usually related to the ability to not suffer arc damage when opened under load. Speed of opening, contact material and quite a lot more may ply a part.
Running an eg 20V switch at say 12V may slightly improve the effective rating and will usually do no harm or lower ratings.
At very low voltages and currents some switches may have contact oxidation problems but that can be disregarded here here.
Even with a resistive load I'd be wary at operating a switch at 80% plus of its rated limit. It might last well, but may not - you are dependant on the manufacturer 'knowing their stuff'. Many do - but many don't.
A filament lamp has a low cold resistance and initial current may be 10 to 20 times the run current. Even at 10x the reed contacts will be overrated by a factor of about 10x. They MAY survive this, but no guarantees. Inrush current can be reduced by "soft starting" with eg PWM or something which switches out a series resistor after a short while.
A Xenon HID lamp CAN have no inrush current with a well designed controller.
Here's a semi randomly chosen HID kit claimed to have no inrush current
An LED bulb or strip of LEDs can, with proper choice, provide somewhat more light per Watt than an HID Xenon system. It need have no inrush current. The best LEDs have > 150 l/W ((lumen per Watt) efficiency ratings. It will take care to achieve this and good commercial finished bulbs may be not vastly better than HID. Bad commercial LED bulbs, of which there are many, have lower l/W than HID.
If you have free access to all wiring points and can run an extra wire then a controlled switch can take the load off the reed contacts. I'd usually use a MOSFET but a bipolar transistor or relay or commercial solid state relay could do the job.
If you have freedom of design choice then a Hall sensor plus current buffer would last indefinitely.
Tell us more and we can advise further.