Center zero movements are mechanically the same, the difference is the way the hairsprings are set to adjust the pointer position.
To modify the meter you will need to get the movement out of the housing - you need to adjust the position of the back hairspring so that the screw fine adjuster on the front one still works. It's delicate work, but doable. The bottom spring mounting can rotate in exactly the same way as the top one (it's used for factory adjustment to get the top adjuster within range).
You need to do it in a completely swarf-free environment - use a big sheet of white paper, also check there's no swarf stuck to screwdriver bits. If you need to remove the scale to get at the mounting screws, then it's a good idea replace it after to protect the needle while you're adjusting. Actually you need this anyway so you can set the center position. make sure the front fine adjuster on the is set mid position so you can adjust the zero when it's back in the housing.
You probably only get one chance of not screwing it up so be careful. If it's a cheap movement then it's less of a worry. If you're not confident with fine stuff then the DC offset may be your only option.