If the load (appliance) was purely resistive like a heating element then yes, a resistor could be placed in series with the load to limit the current and subsequently the power. However, there are a few problems.
Initially you have a 4000 watt load running on 220 VAC so we get 4000 / 220 = 18.18 amps of current. With that we can calculate the load resistance as 220 / 18.18 = 12.1 ohms.
We want to limit the current to the load so we have a 3000 watt load. A 3000 watt load would be 3000 / 220 = 13.64 amps. With that we can calculate the load resistance would be 220 / 13.64 = 16.140 ohms.
So we need to get the load resistance up from 12.1 ohms to about 16.1 ohms. That gives us 16.1 - 12.1 = 4 Ohms. Looks like if we add a 4 ohm resistor we are where we want to be give or take a little. We can't change the load resistance but we can add resistance. However, this seems too easy doesn't it?
With our 3000 watt load the circuit current will be about 13.63 amps. The voltage drop across our 4 ohm resistor will be 4 * 13.63 = ~55 volts. The voltage drop across our original load will be 12.1 * 13.63 = ~165 volts. Our series resistor will need to easily dissipate 750 watts or so but figure 1000 watts minimum so it runs cool. You are looking at very expensive planar type heat sinked resistor in a 4 or 5 ohm flavor. Not very practical but it would work.
There is another problem. All of the above assumes a purely resistive load like heating elements. It does not consider for example a heating element with any type of motor like a fan blower. Since our 12.1 ohm load now only has about 165 volts across it (remember our 4 ohm resistor is dropping 55 volts) that means any motors or fans designed for 220 VAC now only sees 165 volts. The motor may not like this lower working voltage and burn up. Additionally even if it did run it would run much slower than normal moving much less air and now we stand a very good chance of burning up our load. Of course all of that assumes heater elements but I am sure you get the idea.
The best approach would be to have a contactor supply the load and use the timer to drive the contactor. Contactor or SSR (Solid State Relay) would likely be a much more viable solution.
More info on the load as was mentioned would sure be helpful.
Ron