Simply go to
catalog > URL rewrite management and choose "add rewrite" then choose your "custom" from dropdown.
In Request path section enter your
category link (ex. if url is www.example.com/category then enter
and in Target path enter your target url (ex. if blog url is "www.example.com/blog" then just "blog")
Hope this helps.
If you receive
Request Path for Specified Store already exists. then you need to go to
catalog > Url rewrite management and then edit that category by finding it in that grid page.
If none of above work for your try to add redirect in your
Redirect 301 /category.html http://www.example.com/blog.html
For each store magento needs unique identity for
request path, so you cannot add another and by default magento disables
category rewrites request path field. So
.htaccess is the best option here unless you update it from database directly. And good thing with the
.htaccess is you can simply remove it when you need it but if you directly edited your database then will need to edit it again when removing.