Can you go over the 5 watt limit for the trunk light?

I don't think the extra 2.5 watts would be a problem but given the circular configuration, it might not
help much in that application either. Does it have the right base ?
What's the rating on the OEM bulb ??

May I ask what one you have in there now ??

 

You won't blow the ECU or the circuit as the ECU does not drive the bulb directly but simply actuates a relay, which has high current contacts, but I'd worry instead about the extra heat affecting the plastics in the lamp assembly.. I wanted to put brighter bulbs in the front driver/passenger map lights, but the bulbs in there get so hot within seconds that you cannot touch the bulbs with your bare hands.. A brighter bulb will obviously be brighter (duh) but will also put out more heat, and I would worry about melting the plastic or the fixture.. Instead of putting a bigger bulb in, I've gone the way of putting extra lights in: stick on LED strips, panels or pucks strategically placed and then spliced in parallel with the trunk light circuit..

 

If they get THAT hot THAT quickly, then they probably are NOT LEDS and you likely could get a lot more lumens out of an LED that dissipates the same amount of power.......or less.

Your point about being careful about the heat is a good one though.

I'm not too concerned about the "trunk" light but there IS a bad dark spot in the cabin around the cup holders
that might benefit from some stick-on low intensity LED strips.

 

Adding additional lighting is the way to go. I have been very happy with my additions. Check out my post. Unfortunately, I can not link to it here but look under my profile.