My Solar PV system correctly shuts off power during a blackout - I want to safely override that

If your inverter shuts down completely when there is no line power, it is probably not capable of putting out AC without AC present. Some inverters assume the power line is essentially a 0 Ω source. They look at the voltage and decide what current to dump onto it. These types of inverters don't actually synthesize the 60 Hz themselves. They count on that being a input.

If you want to be self-powered during a blackout, you have to get the right inverter for that, which probably costs more. Then the inverter also has to deal with not being able to hold up the line to the proper voltage, and what to do about it. It gets complicated, which is why many inveters require the voltage waveform to already be there.

If your inverter is currently grid-tied, I don't think the anti-islanding feature is something you'll be able to defeat, since it's integral to the safety approval of the inverter (and is a gross violation of most electrical codes)

What it sounds like you need is a separate, off-grid inverter with an automatic transfer switch, that will keep the inverter isolated from the mains when not in use but power your loads after the mains drop out (with some small delay, of course). These schemes generally also involve battery banks to stabilize / provide at least some power when clouds or other solar obstructions occur.

I cannot say for sure if the particular model you've targeted can operate in off-grid mode. (People I know who have this model use it grid-tied.)

Considering the costs involved with a second inverter, you may be better off just going with a gasoline-fired generator for your backup power.

All grid tie inverters MUST disconnect the A/C supply when the grid is lost. This is a safety measure to prevent injuring hydro employees when they isolate systems to work on them. It should be noted that standard procedures require the linesmen to ground the secondary of transformers they have isolated so your inverter will most likely be shorted out if the hydro company is working on your system, maybe damaging your inverter. When hydro finds out you have defeated the safety feature without informing themyou will be immediately disconnected from the grid and it will cost a bundle to get back on, not withstanding any fines you will incur from ESA. However there are grid tie inverters that provide a separate A/C supply that you can power up a few appliances. This is a separate system and is always powered through the inverter. For significant loads you will need batteries to act as buffers to absorb extra power and provide sufficient power for startup, motors typically require 5 times the current to start as they need while operating. So starting your fridge on solar alone will probably not work, it will need a battery to get it going, after its running the current drops back down and the extra power goes into the battery. You can purchase a grid tie/islanding system. It will include the system you have plus a battery bank and an automatic transfer switch(ATS). The setup will insure that when the grid is lost your house is disconnected from the grid and transfered to the inverter. The inverter will then startup in 5 minutes and will run until the ATS detects the grid. At which point the inverter will shutdown and transfer your house back to the grid and startup in 5 minutes. This system insures that the inverter is NEVER connected to the grid when the grid is down. You will need the system properly engineered, inspected and tested before hydro will allow you to connect it. Keep in mind that a backfed pole transformer will provide 13,000 Volts to the primary if you make a mistake, and easily kill your local linesmen. Steve