As other have said it's pretty straight forward. I don't know if they are all like it but on the 3 modules I have done they all have some reset point on the back to bridge before reassembly. I know from experience they don't work right unless you do this so watch out for that.
Has anyone ever changed a G-Shock battery themselves? Is it hard? I have a 150€ watch and the local shop want to charge me 40€ to change the battery.