Probably not.
Anyway, raw output power is not as important as you may think. Especially not if you are getting close to the device’s max, if you push at max, you may introduce more than 1dB of noise level. It is not for nothing that to get higher bit-rates these devices naturally reduce power: from the specs: Pico2HP 1Mb=29dB; 54Mb=23dB.
At least as important, or even more important, is the receive-sensitivity. Can the device listen as well as it can shout? Which is the real reason why the Ubiqity devices are good.
So if you need more, you are better off getting a good antenna (iow, no US$5 ebay junk) and/or good cables than pumping in more power. Personally, I found my factory delivered PicoM2HP antenna better than any of the ones I got of eBay, dispite claims of double gain.. But one I bought in a proper shop did work.
So my advise to you is to not go DD-WRT if that 1dB is your only motivation. You will have to pay a DD-WRT fee, as the Pico is a ‘professional’ device, and you will not benefit. Worse even, DD-WRT comes with the old non-maintained chillispot, and despite Marko’s reassurances, after tracing traffic with tcpdump, I am convinced this doubles your upload traffic (I see each packet twice with tcpdump)