Select all clips on the track, then choose the desired effect.
Some effects will instantly show up on all clips. Others will apply to only the clip whose FX was clicked.
In that case click the "replace effect chain" icon on the toolbar (7th from the left) to replace the effect for the other selected clips. 
The 8th icon will ADD the effect to the other clips. But this process can be touchy and work differently in various VP releases. Experiment.
Be sure to Save AS at each crucial step. Save Project File AS routinely, giving it a unique # or name, so as not to overwrite prior saves. Using Save Project Files (no AS) will overwrite. From the HOME tab, that choice is available by clicking the chevron to the right of the Save Project button on the toolbar.
An alternative would be to copy the track (select all, then <ctrl-C> and paste into a new Sequence - <ctrl-V>. Export that sequence. It's now a single clip that can replace the original track content.