I have very visible veins all over my body. Is there any way of making the veins on my chest less visible? (photo)

Late thromboembolization, years after sclerotherapy is not been described. Once the vein is thrombosed, it scleroses (or scars) and is not likely to embolize months or years later. 

After hand sclerotherapy, I recommend waiting 24 h before performing any forearm or hand exercises. it is unlikely that any subsequent exercising will cause the treated veins to recur. However, hand sclerotherapy carries a small risk of new blood vessels developing in the treated area and back...

Initially, I would recommend hydrocortisone cream (1 or 2%) to be applied several times a day and avoid exposure to the sun for 4 weeks.Once the bliser heals, hydroquinone or scar cream by Plato's Medicinals - see link below. 

I would like to see the extent of the discoloration to better inform you, however the first thing would be to eliminate the venous stasis. You need an evaluation with a Board Certified Vein Specialist. After the stasis is resolved you need to wait. In general venous stasis discoloration DOES NOT...

Most likely after sclerotherapy new veins present themselves. It is possible that a vein that was previously treated and did not go away can get larger if still present, but classically new veins develop.

The pictures show normal veins on your arms. Usually more prominent in individuals that do more exercise like you. They DO NOT  need treatment.