Just to expand on the steps a bit...
Pre-requisite: same
Step A (one time for each account)
- Log in PS4 using a PSN account.
- Make your PS4 the "primary PS4" for that account (Settings > Account Management > Activate as Your Primary PS4 > Activate).
- Log out
Repeat the above for every account that you own: SG, US, etc. (For this particular case, technically you only have to do this step for the US account, since it is the one who's buying things to share. But just do it one time for every account anyway and can forget about it in the future.)
Step B (one time)
- Log in PS4 using US account.
- Redeem the US PSN card code purchased to top up wallet.
- Go to PS Store
- Buy add on(s) you want. In this case, buy the R1 MHW expansion for the R1 disc game. The add-on will apply to the R1 game that's already installed on the HDD. Since this is the "primary PS4" of the content owner (US account), the content (R1 add-on) can be shared with other accounts on the same PS4. (As you probably guessed, on non-primary PS4, contents owned are not sharable.)
- Log out
Step C
- When you want to play, just use SG account to play the R1 game (and R1 add-on that US account bought and shared)
To explain a bit more: Multiple accounts can have the same PS4 as their "primary PS4". As analogy, you own 2 houses, but on your NRIC, only 1 is shown as your primary address. You whole family stays with you in that same house, so every family member also has that same house as primary address. In real life you can have more than 2 houses but for PS4, Sony only allows each account to stay in 2 PS4. In your primary address, things you buy and bring home can be shared with other family members that stay there. The analogy breaks down here but by Sony's rule, things you buy and bring to the other house cannot be shared, only you can enjoy them.
Before you spend any real money, note that the US/R1 has a bunch of free stuff (
link) Make the US account, then grab these freebies, install them, see if you can find them in the game.
Questions:
- Does the game have a local save file on the HDD or is the save kept on the server only?