What is called a foo dog is actually a lion. They can be thought to symbolize the state of buddhahood. In Chinese the buddha is call "Fuo", which sounds like "foo". I've never seen a foo dog with a spear. The male almost always holds a hollow ball engraved with interlocking circles. This symbolizes the buddha's dominion over all creation, and the realization that the universe is interlocked into an unbroken whole. If you want to change the symbolism, then you probably are not really drawing a foo dog, but rather just a cool looking animal. It wouldn't bother me.
The foo dogs at temples never have a collar, but often are shown with collars at government buildings. This shows that the government officials considered the religious truth to be subservient to the secular truth. Because foo dogs are ubiquitous in both sacred and secular usage, I don't think you would offend anyone with your tattoo.