Great question and welcome to the forums!
Trichomes are one of several ways to decide when to harvest. You'll take into account the overall look/stage of the plant (ie. are the leaves fading, have the buds stopped fattening, etc.), what the pistils are doing (have they stopped putting out new white hairs, are they orange/brown, and shriveled up), and lastly the trichomes. When it comes to using trichomes to help decide when it's time to harvest, you'll get different opinions, but most will say to harvest at some point when they are mostly cloudy and up to 10-15% amber.
Now to your question. You're not way off, especially because of the way many articles about this topic are written. Many are written with the undertone that you can change the effects of your bud, but really they are just illustrating what will happen if you harvest too early or too late. You won't be able to get a completely 'opposite' experience from whatever the genetics are and using 'indica' and 'sativa' to describe the effects isn't always accurate rather it's a convenient way (even if erroneous) to lump different genetics into an extremely generalized category. However, if your strain produces more of an up effect, harvesting later (more amber trichomes) might make it a little more chill and vice versa if you're growing genetics that have more of a relaxing effect and you harvest on the early side. My recommendation is to harvest in the middle of the window to get the effects that the breeder says you'll get. That's usually when most/all of the trichomes are cloudy with up to 10-15% amber. If you want a relaxing effect, find a strain that does that and if you want a more uplifting effect get genetics that are known for that regardless of if it's an indica or sativa since most strains today are hybrids of both.
Basically what's happening with the trichomes is that different cannabinoids are being produced (or degraded) as they change from clear to cloudy to amber and it's important to remember that it's all of the cannabinoids, terpenes, etc. that create the final effect of your buds. However, you can use this to your advantage when you decide what kind of experience you're looking for.
Good luck, great question, have fun, and happy growing!