Here is a patch which allows you to save your created maps in the edit mode via SRAM. The patch creates an SRAM for the ROM and also changes the mapper from NROM to MMC4 as well. The original title screen has also been replaced with a more detailed one by the author.
Lode Runner (Japan).nes - NOINTRO
CRC32: 68224C5C
MD5: 739B7C1DB2B397941C1260999B641A7F
SHA-1: 581A3E9AD5FFD985E21738E18189C67B4E0A516C
SHA-256: 46339E669EB67B448A563AFE13B30007C16DEC0A0B097684AE2B44EB7626D971