Modifying Magazines to Limit Capacity

[def90]

The law only states that you may not buy or assemble a magazine over 15 rounds so yes it is legal for an individual to assemble a 15 round or less magazine.

Though I haven't quoted the specific verbage if you read it it is pretty clear, I don't see where there is any ambiguity.

As for "permanent" modification vs non the term in general for most firearms related things has meant that the item in question cannot be reverted back without using tools. A loose block in a magazine could be considered easily convertible as all you would do is remove a base plate without any tools and pull the block out, a rivet would likely be considered a permanent fix as it could only be defeated via using tools such as a drill which would then be interpreted as you physically modifying an existing product.