Changing POV style mid-story

Question

I'm writing a story that is told by the main character. The idea is that at some point, he decides that what has happened merits documenting, so he's telling part of it in the past tense. The problem is that I want him to develop into an unreliable narrator as the story progresses into the future, so I need to have him eventually "catch up" to "now" and start documenting events as each day progresses.

To keep it sounding believable, that means the POV/tense will have to shift a bit, from narrating a series of events in the past, to writing what amount to "journal updates" in the present/near-past. One has the benefit of perspective, the other does not. For example:

Little did I know what would be the consequences of my decision...

Versus

I just had to keep on walking and hope nobody noticed...

Two descriptions of the same scene, but one has hindsight while the other is blind. Will that change-over mid-way through the story be jarring or distracting? Should I rework it so I don't have to switch perspectives?

TL;DR: Will switching perspectives from past to present partway through a story cause problems?

Answer 1

It's not particularly difficult. Tense is a tool feared by too many aspiring writers.

What you appear to be asking can be seen in Forrest Gump (film).

I am sitting on a bench waiting for a bus (present). Whilst I'm waiting I will relay to anybody who wishes to listen events that led me to this point in my life (still present).

My momma was . . . (past).

And that's all I have to say about that. (present).

Jenny was the sweetest thing I'd ever seen. Me and her was like peas and carrots . . . (past).

And that's all I have to say about that. Blah, blah, blah . . . (present).

Bubba was my best good friend . . . (past).

This is format for the story until shortly after the midpoint. All scenes where he's sitting on the bench are in present tense. Until he discovers he can walk to his destination. At this point there's a reset, a narrative, and the clock starts. The moment he leaves the bench, events that occurred on the bench are now in the past. It's clever in a simple way: the story is told in a combination past and present tense within a past tense framework. He's going to meet Jenny (present tense according to his narrative tense) but according to the overall story tense - this is in the past (Jenny died of aids).

The art of writing is this way is that you have to do it well - nobody will notice your genius unless they analyse it.