Tested this with Nox emulator. GameGuardian DOES change the values client-side, however this DOES NOT change anything server-side. I can set my ATK to 99,999 and still do the same damage as before. I assume this was fixed in 1.0.3.
Game Name: Grand Summoners
Game Version: 1.0.3
Google Play Store Link: Store Link
APK Link: APKPure
Cheat Requested
0 Energy Costs on Quests and Exploring
Instant Arts
Daily always open
Explore no key cost
Have you tried any cheat engines?: LuckyPatcher
GameGuardian