Hope you don't mind a long-ish reply :-)
Personally, if not testing wouldn't jeopardize my HB plans, I would not test. Meaning, if my MW was required to treat me as GBS positive unless I tested otherwise, that might be a reason I would test but otherwise I'd decline it. Either that, or I'd ask for a urine test instead of a swab; more on that below.
First off, this page has a ton of great info and resources -- http://www.gentlebirth.org/archives/gbs.html -- I suggest you check it out if you haven't already.
I was GBS positive when I had my son. That was with care from CNMs in an American hospital setting. DS being my first, I didn't know the first thing about GBS or what having it even meant. So with no thoughts on the matter whatsoever, I did the vaginal/rectal swab thing they do around 32-34 weeks. It was positive. My MW explained how the protocol was that GBS positive moms are supposed to go right to the hospital if their water breaks, and that they get IV antibiotics during labor. Never having labored before, it sounded like NBD to me. Only after that positive test result did I read up on GBS. As fate would have it, a couple days before my EDD my water did begin to leak (not a full on gush). At least by then I knew enough about alternative approaches that I felt comfortable buying myself a little bit of time at home to see if labor would start in earnest before clocking-in at the hospital where they'd want to deliver DS within 24 hours. So I started myself on a super vaginal-cleanliness aware protocol and dosed up orally on echinacea, garlic, and vitamins C & E. A day or two later I was still leaking and not contracting in any significant way. At that point, I called my MW and went to L&D where I got IV antibiotics and some prostoglandins to jump-start labor (thankfully I avoided pit and all other drugs from there on out). The IV was a huge PITA. It really affected the way I could labor. It's like if I could change just one thing about DS' birth it would be to get that thing off my arm. In the end, my MWs were cool about the timeline, they were fine with my decision to decline the pit and labor at my own pace. DS was born more than 24 hours after I got to L&D and a day or two after I started to leak. He was totally fine, no GBS complications or anything like that. Was that the antibiotics or was it that he wouldn't have gotten it anyway? Who knows.
So with that experience behind me, GBS was on my radar with this pregnancy. But this time I'm having my baby in the UK where clinical practices differ from those in the States. Still, the setting is kind of similar to my last birth. I'm with what's basically a CNM and plan to deliver at a birthing center co-located with a hospital. One thing I found interesting is that here they don't do the 3rd trimester swab test, they do a urine test in the 1st trimester. As I understand it, many more women will pop positive on a swab than on a urine test. But if you're positive on the urine test that probably means you're extensively colonized and therefore at a higher risk of passing GBS on to baby. So there's two different "positive" thresholds for these two different tests. A few months ago I did consent to the urine test, figuring if I'm that extensively colonized I want to know it. In the two weeks leading up to the test I followed some of the recommendations I found through the website above. Basically I was on cleanse-type diet (modified to meet my nutritional needs during pregnancy, as in I might need more protein but I certainly didn't need cookies), did all sorts of vaginal remedies like TTO, garlic, hydrogen peroxide, and ACV; and took probiotics, ACV, echinacea, and garlic orally. The day before the test and the day of the test I did a diluted chlorhexidine wash (the best part was buying it at the feed store...um, I need this special soap...yeah, sure, for my dog). Who knows how all that affected my flora but I did test negative. Because GBS can come and go, I plan to repeat that protocol (probably in a slightly more relaxed fashion) starting a week before my EDD.
There's some interesting research out there about chlorhexidine as a vaginal wash during labor when GBS is present, in lieu of IV antibiotics. It's a hardcore chemical but with a pretty low level of invasivness and totally do-able at a HB. There's also some research on giving antibiotics orally or by injection instead of as an IV. I can't remember the particulars, but as I recall that approach didn't sound super promising.
IMO this is one of those hard "N of 1" choices. It goes without saying that I would be devastated if my baby is the one in ___ who dies from GBS complications. But does that justify a policy of interventions, interventions that carry their own risks, for the other ___% who will be fine? I don't know. I think we each have to decide for ourselves. And it's a really hard choice when what we think/feel/know/believe will keep ourselves and our children safe doesn't always align with laws and institutional policies.
Good luck. Let us know what you decide and how it all turns out. I'd be curious to hear your MW's take on the situation too.