Hi Aaguilar,
This all depends on what species of juniper you're working with. The Chinese juniper that is commonly called shimpaku will revert to needle foliage if it is stressed or if it is pruned quite hard or at the wrong time of year. On species where the mature foliage is soft, scale foliage (like shimpaku), the juvenile foliage is often a needle form. There are other species, like needle juniper (tosho), that stay in the needle form. There are still others, like the San Jose' juniper, that generally have a mixed foliage form, never 100% one of the other.
Hope this helps a bit.
Kind regards,
Andy Rutledge
b u n j i n | d e s i g n ::
www.bunjindesign.com
zone 8, Texas