When you repot an orchid, you stress the plant.
Most repotting is recommended when new roots are expected to be produced. This is where you would want the plant to expend energy in accepting the new media and initiating new growth.
If your plant is in spike, it is generally in a different phase of growth and if repotted may abandon blooming and shift over to root growth etc.
Unless your plant is in danger with poor media, I recommend waiting until after it blooms.
Having repotted many plant with spikes/buds, about 50% of the time I've done this I've lost the blooms...but I accepted the risk because I felt it was best to repot the plant then