I totally agree with Sue. Its good to make it your own if you use someone else's spell. Its best to add though and not subtract from it. You never know if you are removing an important portion of the spell. Some are very carefully formulated.
A spell written by a particular person carries the energy of that person. If they are good and experienced, its not a bad thing, but if you have no idea who wrote the spell originally, then it is best to alter a few things to disconnect it from the creator and connect it more personally to yourself!
Spells I pm to people here are always mine unless I refer them to another source. I feel that when I consent to a spell being used by another that I am lending a bit of my own energy (my spell) for their purposes. I refuse to put my spells in the spellbook because I have no control as to who is using them and I don't feel comfortable with that.
I'm an artist, so I have a firm belief that when someone creates something with their heart in it, it's a part of them in a deep sense. When you look at a Van Gogh painting you are getting a peak of the way he perceived the world, how he thought. Every stroke was his design, premeditated or naturally flowing. If someone else tries to paint that same picture the exact same way, it is only going to be looked at as second best to the original. But when they use their own style to paint the same subject, it becomes their own. And spells are no different.