To modify low-level data on a device like the MC801A, one would generally need to enter "Maskrom Mode" or "EDL Mode" (Emergency Download Mode). This requires shorting specific points on the device's motherboard physically. This process is incredibly risky for anyone without soldering skills and advanced knowledge of embedded systems. One wrong connection can permanently destroy the router.

The core steps, as gleaned from these guides, are:

The IMEI is stored within the device's non-volatile memory, specifically inside the (Non-Volatile Random-Access Memory) or EFS (Encrypting File System) partitions of the Qualcomm modem chip. This data is protected by secure boot mechanisms to prevent unauthorized tampering. The Role of Qualcomm Diag Mode

However, altering an IMEI carries significant legal, ethical, and technical risks. Legal and Ethical Compliance

A clean, valid IMEI from a disconnected or old smartphone that you own. Never use a blacklisted or active device's IMEI. Step-by-Step Technical Overview