Yes, Decolour Stripper is an ideal product to apply to dark regrowth to lighten the base safely. Always remember to mix and apply from a plastic bowl using a tint brush. Apply to dry hair only (not damp) onto just the dark regrowth. If you like a very shade specific blonde result, once the roots have been lightened, you can apply a second process blonde colourant onto the newly lightened areas, to create a deeper or more tonal blonde shade.
If your dark roots tend to be stubborn at lifting, apply Decolour Stripper then loosely wrap a sheet of tin foil over your hair, creating a loose cap. This foil cap can be easily removed to check development and then placed back on if further development is needed. However, creating a foil cap will trap heat next to the roots and boost lifting.