Hell's yea, if you provide all the schematics and parts list
I'm always down for a little tinkering.
The BOM is here:
Partlist for 12V/12A SLA Charger
R1 1R8 (2W)
R3 0R2 (5W)
VR1 470R trimmer
D1, D2, D3, D4, D6 and D7 BY550
LED1 Red or green LED
IC1 LM338-TO3 (on heatsink)
PB1 Momentary action Push Button Mains Rated Switch
X1 4-way Screw Terminal Block
X2 2-way Screw Terminal Block
X3 2-way Screw Terminal Block
If you cannot find a relay that fits into the PCB, or if you have another 12V activated relay with mains rated contacts (SPST, SPDT or DPST would all work as well), tell me and I can change the pads into whatever measures you give me - I just found a random relay for the layout.
The PCB can be cut along the white line and mounted as a "sandwhich" C1A should be connected to C1B etc. and not with a too thin wire (mains wire would be fine), whether you cut it or not.
The BY550 diodes could be BY550-50, BY550-100 etc. and could be replaced with any other 5A diodes.
Any questions I haven't foreseen, just say so.