The v1.0.2 update primarily focused on fixing "soft-lock" bugs that could prevent players from progressing:

The file size for the base XCI is approximately 4.1 GB, so ensure you have adequate space on your SD card or drive. Is it Legal?

Enhanced the pairing process between the Nintendo Switch and the Pokémon GO mobile app. Gameplay Mechanics: A Fresh Take on Tradition

The "Pokémon Let's Go, Pikachu! XCI ROM - Base v1.0.2" you're referring to seems to be related to a specific version of a Pokémon game ROM, likely for emulation purposes or discussion within the context of Nintendo Switch games and their ROM (Read-Only Memory) counterparts. Let's break down what this entails: