You don't have to remap them for the LN difficulties. There's 2 LN types in the bml format and the converter only does the first, outdated type. Nearly all maps these days uses the more recent 2nd type. You can open the map and change all the LN-type 2s to LN-type 1s and save it as a .bms or .bme. Then the converter will successfully covert all the LNs.
The issue is the fastest way of doing this is group selecting them in iBMSC and changing their types in the convert menu, but you can't do that if single notes are present since that will turn the space between that single note and the next into a long note. In those cases you have to convert the LNs to the older type one by one... Which is a pain, but faster than remapping the whole map.
The issue is the fastest way of doing this is group selecting them in iBMSC and changing their types in the convert menu, but you can't do that if single notes are present since that will turn the space between that single note and the next into a long note. In those cases you have to convert the LNs to the older type one by one... Which is a pain, but faster than remapping the whole map.