How to multiply each pixel of a ImageCollection by a single value

Yes it is possible by using a .map() call.

test = ee.ImageCollection([ee.Image.constant(5), ee.Image.constant(10)])
val = 2
test_multi = test.map(lambda image: image.multiply(val))

print(test_multi)

Let me know if this works. I'm mostly working in the javascript editor, but the conversion to Python should be quite straight-forward.