HTC Warranty with unlocked bootloader

Hi,I want to install custom rom. (like most people) but, With htc one m7 I used the warranty, so, I want to be able to use it with the M8. My question is. to return full stock, its need s off right? Right now I cant afford 25 for the soff (in my country, outside of USA is a little more difficult because the conversion). So, if I use the dev unlock bootloader, Can I install custom any rom ( i ask because I dont know where I saw custom rom requiring S-OFF) and then do the s off after a while (maybe 2 o 3 months). If I use dev unlock from htc, they will be able to track that I install custom roms? And how about bricks, wich side is safest (only unlock bootloader or Soff) and wich side is more easy to recover?.

Thanks in advance