Please, no. Go through the proper channels like everyone else. If you have a referral - great. Otherwise, DON'T spam current employees you randomly find on linkedin or whatever. I get those from time to time and ignore 100% of them.
Much like many other decisions you're making in the job market, it's a polarizing choice that increases your overall chances when the alienated class of people isn't too large. If 90% of people ignore those emails but your chance of getting a first-round interview goes up 5x compared to a cold application when the remaining 10% respond, 2+ emails are easier to send than 1 application, especially when you've done the legwork to make your application any good.
I haven't used techniques like these specifically yet, but as somebody who nearly always eventually gets the job once I've had a first-round interview, I wouldn't be opposed to seeking out the hiring manager and contacting them directly to decrease the resumé false rejection rate.
There are more effective ways of spending your time than that.
I'm not sure in this day and age. Your goal is to get in front of a human, and that's harder than ever. If you spend hundreds of applications with no response, even a "You're blacklisted" response from a human will feel better than the cold neglect of today.
It's not zero effort, but I argue it's less effort than being months into your search and trying to find another 20 companies that you seem to be qualified for. Having the human element can also be encouraging too instead of the 50th dang workday application.
Exceptional folks rarely limit themselves to pushing submit to upload their CV. That proper channel is a lottery, and they know it. It's a broken system that requires hustle to increase the odds.