I have a retaining wall that starts at on end at 1 tie , goes to 7 in the middle, then ends up at 1 again. About 100 feet long with a fence above most of it. ( 6 foot cedar stockade fence.). The ties are rotting and dirt from my yard is coming down into the neighbor's yard. We wish to replace the wall with a stone wall used for retainers these days. My question is, can you leave the railroad tie wall and just build up against it? What would be the consequences of doing that. Thanks, Bill Spencer

Sure, if you have room between the two walls for gravel, and go below grade far enough for a footing as defined by the material you use.
By 'stone wall used for retainers these days' do you mean manufactured interlocking blocks? Those walls can only be about 3' high. The pressure on a higher wall will be enormous.
I can't envision your wall somehow.