Set Balance of the 3 major stables (DAI, USDT, USDC) on Arbitrum forked node, via Anvil/HH setStorageAt.

set_balance_arbitrum.sh

import { ethers } from "ethers";

async function setBalance(account: string, token: string, slot: number){
    const paddedSlot = ethers.utils.hexZeroPad(ethers.utils.hexlify(slot), 32);
    const paddedKey = ethers.utils.hexZeroPad(account, 32);
    const itemSlot = ethers.utils.keccak256(paddedKey + paddedSlot.slice(2));
    const storageSlot = ethers.utils.hexStripZeros(itemSlot);
    await ethers.provider.send("anvil_setStorageAt", [
      token,
      storageSlot,
      ethers.utils.hexZeroPad(ethers.utils.parseUnits('100000000').toHexString(), 32)
    ]);
}

async function setBalances() {
    let account = "YOUR_ACCOUNT";

    let dai = "0xDA10009cBd5D07dd0CeCc66161FC93D7c9000da1";
    let usdc= "0xFF970A61A04b1cA14834A43f5dE4533eBDDB5CC8";
    let usdt= "0xFd086bC7CD5C481DCC9C85ebE478A1C0b69FCbb9";

    setBalance(account, dai, 2);
    setBalance(account, usdc, 51);
    setBalance(account, usdt, 51);
}
setBalances();