There aren't any triggers at the moment although I think Gary may have plans for one.
Greening-up is a little tricky if you have a lot of positions that have opened and closed and Gary has published an example spreadsheet that includes a green-up facility that you may find useful.
Have a look here:
http://www.gruss-software.co.uk/forum/viewtopic.php?t=4659
Be careful though with greening up too close to the off with greyhounds. As there is such low liquidity on most races, you can find yourself with open bets when the market suspends. It may be better to give yourself a bigger window and to attempt to green up several times to ensure that you close everything.
HTH
Kiint