I read a series recently, and by read I mean that I made it through three out of the four books, where the author employed the use of first person, third person, and past and present tense. The first book followed a girl from the Germanies, before the various areas united into one Germany, and as such it was written in third person-past tense. The second book picks up when she's thrust into the future, in Africa. Told from the African boy's perspective, it's written in third person-present tense, I believe. Book three slips between the two as some chapters are from the girl's perspective, and others from the African's more present perspective. All of that I could handle, but once book four took on first person-present tense, I put it away. (As a side, it didn't help that in the first two books, the mentally heard voices of the dragons who traveled with them were differentiated by font types, a trait dropped by book three to cause nothing but confusion, and perpetuated in book four with the infuriation of first person-present tense.)
Now, I can enjoy some first person stories when executed well, my favorite example being Jacqueline Carey's Kushiel's Legacy and the Imriel Trilogy that follows, and despite being known to occasionally dictate my actions in first person-present tense, I can't actually tolerate reading it for more than a few sentences. I've not yet sat down to analyze the whole why of it, but something just crawls under my skin and makes me want to claw out my eyes when I read it. . . . Maybe I'm over reacting. o__o
What I mean to say is that I've seen the different tenses and POV's used to indicate that a person is from a particular period of time, e.g. the German girl gets past because she's from the past, the African gets present because he's from the present. It makes literary sense. So I've seen it done, and felt that it worked, even if I couldn't finish reading the project due to personal taste levels. I think that if you DO change tenses that you try to do so to illustrate a difference in perspective or time period, or it can become very cumbersome for the reader to slog their way through.
Related aside: It's like a movie I watched (part of) several years ago about the Cuban Missile Crisis. Certain scenes would start in black and white and slowly fade to color, while others would start in color and become black and white. For the life of me, I could find no reason for it. It wasn't a dramatic situation that caused the B&W scene, it wasn't every scene that started that way. Release of tension wasn't what brought color back . . . . The lack of obvious reason for these changes was distracting from both the acting and the story, to the point that it didn't matter how good either aspect was, I had to get up and leave because the color-no color inconsistencies made it too difficult for me to simply enjoy what was going on. So, don't replicate that in words. :-| That's my advice.