Most people no longer recommend switching fertilizers. The old idea was to switch from a regular fertilizer to a so-called bloom booster to induce buds. You already have a spike. Plus it has been shown switching fertilizers isn't necessary.
You can cut off the old spike at any time, or leave it. I like to leave old Phal spikes, because they may grow and bloom again.
__________________ May the bridges I've burned light my way.