If I had chemical glassware, simple chemicals, and MHRB in my house I would say with complete confidence that I intended to experiment with extracting dye, mostly as a hobby, but also because I thought it might possibly be a business opportunity. I could shown them internet sites that mention the dye characteristics of MHRB.
And, that would work just the same with your "story" as you describe it regarding cactus: "Hey, this isn't peyote--I've seen peyote on the internet and this doesn't look ANYTHING LIKE PEYOTE."
AND...if the bastards happened to CHECK MY COMPUTER, I'd tell 'em that YES, I actually first heard of this MHRB stuff on the crazy NEXUS DRUG SITE where I pretend things...and that's how I learned about it, got interested, looked it up, and saw that it made a unique color dye!
But, kidding aside, our COMPUTERS can be our biggest enemy. There are programs available that can wipe clean all files related to internet use, AND REALLY wipe clean empty areas of your hard drive, by overwriting them with 0's and 1's. My only worry would be a search warrant--and I don't think I've done ANYTHING that could legally permit one to be issued. The one exception might be this site: If they can show that YOU (by your IP address) are actively involved with discussions about producing illegal substances, then a warrant probably COULD be secured for a search. But let's remember that the server for this site is in (I think) Holland--happy news for all of us not living in Europe). HOWEVER, it's very unlikely local LEOs are as stupid as HYSTERIX, who seems to think we're a HUGE manufacturing partnership--ALL OF US! Cops in fact has almost no incentive to go after individual users--especially in their own homes...at least without the complaints of neighbors.
For me, if the nexus suddenly went offline for more than a day, I'd probably want to hide any extracted substances offsite until things seemed clear. Otherwise, there's probably nothing to worry about....except friends/girlfriends/relatives/wives who suddenly decide they want to hold a grudge.