I'm pretty sure that launching into RCM itself won't be detectable, but launching CFW while connected to the internet might be, no matter what you're doing (EDIT: I believe launching CFW on your main NAND at all without doing any kind of clean NAND restore from a blank dump can get you flagged the next time you connect to nintendo's services).
Safest is to execute RCM, go into a CFW loader such as SX Loader / Hekate / Atmosphere and do a dump of the NAND (the flash chip that stores the switch's firmware) to your installed SD card and possibly enable AutoRCM. With AutoRCM enabled, the switch won't boot into Horizon without the USB-C dongle from TX or connecting it to a PC or android phone and using an RCM app, but you also don't need to use the jig every time. If you plan to switch SD cards around in order to play legit and go online, I'd recommend against using AutoRCM but to be very careful about how you're booting, if you have wi-fi enabled on the system, and which SD card you have installed.
With all that, you should be able to set up android on there and/or use CFW on EmuNAND (running that NAND dump you did before from your SD card). As long as you don't connect to the internet with CFW you should be fine.
Plenty of guides on GBATemp and across the net to help you do things smart and safe.