Yes, there are many ways to make isomers--it is done commonly in the pharmaceutical industry. Can be done directly via synthesis, or a racemic mix can be separated by physical processes such as crystalization or enzymatically. Most enzymes have a chirality (like the glove analogy), so they tend to create produces with a single isomer.

This said, making an organism with mixed chirality would likely not be effective because, likely, many reactions would not proceed or would proceed with poor efficiency. All D- or all L- would work fine, but any evolved organism would suffer/die with a mix of D- and L-.