Using the following method, you can activate a 30-day trial of ESET Smart Security Premium, indefinitely.
Only tested on Windows operating systems.

1.) Reboot Windows into Safe Mode (you wont be able to do this in the live OS).

2.) Start your registry editor (regedit) and edit and remove all information from the following keys:
Code:
[HKEY_LOCAL_MACHINE\SOFTWARE\ESET\ESET Security\CurrentVersion\Config\plugins\01000006\settings\Ekrn\Check]
"CfgSeqNumberEsetAccGlobal"=-
"DNSTimerSec"=-
[HKEY_LOCAL_MACHINE\SOFTWARE\ESET\ESET Security\CurrentVersion\Config\plugins\01000006\settings\Ekrn\Ecp]
"SeatID"=-
"ComputerName"=-
"Token"=-
[HKEY_LOCAL_MACHINE\SOFTWARE\ESET\ESET Security\CurrentVersion\Config\plugins\01000006\settings\Ekrn\Info]
"LastHwf"=-
"ActivationState"=-
"ActivationType"=-
"LastActivationDate"=-
[HKEY_LOCAL_MACHINE\SOFTWARE\ESET\ESET Security\CurrentVersion\Config\plugins\01000200\settings\stProtocolFiltering\stAppSsl]
"uRootCreateTime"=-
[HKEY_LOCAL_MACHINE\SOFTWARE\ESET\ESET Security\CurrentVersion\Plugins\01000400\ConfigBackup]
"Username"=-
"Password"=-
"LegacyUsername"=-
"LegacyPassword"=-
[HKEY_LOCAL_MACHINE\SOFTWARE\ESET\ESET Security\CurrentVersion\Config\plugins\01000400\settings]
"Password"=-
"Username"=-
[HKEY_LOCAL_MACHINE\SOFTWARE\ESET\ESET Security\CurrentVersion\Config\plugins\01000600\settings\DistPackage\AppSettings]
"ActOptions"=-
[HKEY_LOCAL_MACHINE\SOFTWARE\ESET\ESET Security\CurrentVersion\Config\plugins\01000006\settings\Ekrn\Info\LastHwInfo]
"ComputerName"=-
"Version"=-
[HKEY_LOCAL_MACHINE\SOFTWARE\ESET\ESET Security\CurrentVersion\Info]
"EditionName"=-
"FullProductName"=-
"InstalledByERA"=-
"ActiveFeatures"=-
"UniqueId"=-
"WebActivationState"=-
"WebSeatId"=-
"WebClientComputerName"=-
"WebLicensePublicId"=-
"LastActivationResult"=-
Alternatively, you can copy and paste this code into a .reg file and import it using an elevated command prompt.

3.) Navigate to C:\ProgramData\ESET\ESET Security\License and delete the license.lf file.

4.) Reboot into your live Windows OS.

5.) When ESET starts, bring up the main ESET window and it should prompt you to enter a license key, login to an ESET account or start a trial.

6.) Select start a new trial and the next window will ask you for an e-mail address. Do *NOT* use any previous e-mails, instead use https://temp-mail.org/en/ or a similar service to generate a temporary disposable e-mail and enter that one instead. Continue through the prompts until it says ESET Smart Security Premium trial active.

CONGRATULATIONS! You have another 30 days of full protection from ESET. When it is due to expire, rinse and repeat. Set a calendar event to remind you every 29 days so you know when it is due.