Quick question: Do I need to repot indoor bonsais in the spring as well? Or can it be done all year round like fertilizing them?

Indoor bonsai..
You can repot plants as long as they are actively growing. So plants that you keep indoors -hopefully tropicals- can be repotted yearround. However, that being said.. They are strongest when they are outside receiving full sunlight in early spring. I would avoid repotting in early winter/late fall where possible unless you know very well what you are doing, and your plants are in a sunroom.

Yes my ficus is lighted with metal halide lamp. That why I thought it does not make sense to wait spring as it is vigorous all year round.