Relay to control mains

Yes it is possible. One way to reduce the risk is to oversize the relay, such as 20 A rated contacts for a 5 A load current.

ak

If the mains load that you are controlling is made to the normal safety standard, it shouldn't matter that if the live remains connected.

It would only matter if the load had exposed parts that someone could touch that were connected to neutral.

All mains equipment should be made with live and neutral both insulated to protect against the full mains voltage, as all it takes is a broken neutral connection somewhere for live and neutral to be at mains voltage.

When working on mains powered equipment, after turning off you should always confirm that it is isolated, either by measuring the voltage to earth or by unplugging.

Residential protection for single line (L1 or L2) loads is only done with single pole breakers because Neutral voltage rise is designed to less than 5% at shared wiring and breaker loads. Although there is no problem using DPDT, it does not increase reliability of the switch. I speculate it may decrease safety to the user who thinks the power is off if/when the line contact is welded but the neutral contact opens.

If you are asking about the risks of a live neutral, I wonder if you are aware of how to protect and de-rate relay contacts with reactive loads that may have 700% rated surge currents and arc energy that reduces switching life rapidly by orders of magnitude. For example snubbers may be internal or external resistance to plastic film capacitors such as 100 ohms + 100 nF for a 10 ~15 A relay.

Reliability also improves with more conservative ratings as suggested by ak. Using the full rating of a relay is never a good idea for long life expectancy. A well designed relay with rated reactive loads may last 10k cycles.

AnalogKid, I'm using the highest rated relay, but I have no control on the user side and the user might decide to connect an oversized load.
Diver300 yes, I assume the powered device is designed to meet the safety standards (both live and neutral insulated), but if only one pole of the relay disconnects the user might think there is no power as long as the device is not running and he might decide to disassemble the device. For example, the user might decide to control a bulb and he sees that the bulb is not emitting any light so he believes there is no power and decides to change the bulb. Although the bulb is insulated and meets the safety standards, once he decides to unscrew it, he creates a hazardous situation. Usually, domestic light commutators are installed on the live wire and once you put the commutator in the off position the bulb is not powered any more, but in my case I don't know which wire will be live or neutral (the European plug can be connected in any position), so the only solution I came with is a double pole relay which is still hazardous if one pole gets stuck.
Tony Stewart, I am using a 40A relay, but if the user decides to connect an inductive load, the relay can be damaged no matter how big it is. Just a fuse is not a solution because it should be installed on the live wire, but I have no control over wires, live can be swapped with neutral at any time.

Of course, the user would be blamed for changing a bulb without being sure there is no power or plugging an oversized load, but I think the best approach would be to design the device with some sort of protection and not blame the user.
If this situation can be anticipated, I think the best approach would be to design some sort of protection.