Okay, now let's break it down how you find the answer.
That $0210 area is suspicious. Especially if you look at the first 4 sprite entries (that is, the first 16 bytes at that spot)
Notice that for sprite 1 ($0214-0217), the Y ($0214) is the same as sprite 0 ($0210) and the X ($0217) is +8 (right one tile) from sprite 0 ($0213), Sprite 2 will be +8 in the Y ($0218) and +0 in the X ($021B), sprite 3 will be +8 in the Y ($021C) and X ($021F).
So now open the debugger menu and click Breakpoint. You want a WRITE on the CPU. CPU address $0210. You know it's going to write the value 0x57 from that. So reset the game and get to the title screen. (click Run when the debugger window opens to skip other writes) As it's about to load the title screen, notice when it tries to write the value 0x57.
0F:FC94:B1 C4 LDA ($C4),Y @ $96CD = #$00
0F:FC97:65 CA ADC $00CA = #$4F
>0F:FC99:9D 00 02 STA $0200,X @ $0210 = #$F0
STA means it's trying to STore A to $0210 (the @ $0210 part), and A is 0x57. So it's probably the right value.
That LDA above is reading from $96CD. That is a ROM area, so we can figure out what ROM address that maps to.
I think you can just open FCEUX's hex editor, scroll to $96CD and click "Go to here in ROM" or something. Else look at the data and do a hex search for data in the ROM. Either way it comes to $2B6DD.
Looking at the data it's 00. Interesting data but not a 0x57, so that means RAM address $00CA is probably something we should look for. (because it's reading from the table at $2B6DD, adding the value at $CA)
So, let's reset the game and set a new breakpoint for WRITE on $00CA.
0F:FC35:A5 CA LDA $00CA = #$00
0F:FC37:30 0C BMI $FC45
0F:FC39:79 03 03 ADC $0303,Y @ $03E3 = #$4F
>0F:FC3C:85 CA STA $00CA = #$00
Adding from address $03E3. That's a RAM address.
Needs another breakpoint.
0A:9E89:A9 00 LDA #$00
0A:9E8B:8D E1 03 STA $03E1 = #$00
0A:9E8E:8D E4 03 STA $03E4 = #$00
0A:9E91:8D E5 03 STA $03E5 = #$00
0A:9E94:A9 50 LDA #$50
0A:9E96:8D E2 03 STA $03E2 = #$50
0A:9E99:A9 4F LDA #$4F
>0A:9E9B:8D E3 03 STA $03E3 = #$4F
LDA #$ means it's reading an IMMEDIATE, or in this case hard-coded value. So we just need to find this code in the ROM and change the #$50 (X) and #$4F (Y).
We come to $29EAA for the #$4F, so that #$50 is going to be at $29EA5.
Though as it turns out, Mother displays a static frame of the earth in the tilemap, behind the spinning globe sprite.
So you'll have a tilemap to find and edit (if you haven't already) or you'll have two earths.
I recall EarthBound had some hacking protection on the title screen (the cause of the infamous "piracy" screen), but I'm assuming you know that already.