There are two things to compare here: series and models.

Series
The discontinued DTX400 Series is based on the DTX400 module and has three models: the DTX400K, the DTX430K, and the DTX450K.
The current DTX402 Series is based on the DTX402 module and has four models: the DTX402K, the DTX432K, the DTX452K, and the DTX482K.

The models in the DTX402 Series have these advantages over the DTX400 Series:
- the DTX402 module has more voices than the DTX400 module
- more natural-feeling drum and cymbal pads
- chokeable crash pad
- a redesigned rack that is sturdier and more stable

Models
The DTX402K model has these advantages over the DTX450K...
- DTX402 module
- chokeable crash pad

... and these disadvantages:
- single-zone snare pad
- silent kick unit

The DTX450K model has these advantages over the DTX402K:
- 3-zone snare pad
- real bass drum pedal + kick pad combo

... and these disadvantages:
- DTX400 module
- non-chokeable crash pad

My opinion
I'd go for the DTX450K because I think the DTX402K is too basic. In my opinion, the DTX450K's bass drum pedal + kick pad combo and 3-zone snare pad are essential, must-have features.

OP just copied a post from this forum,
https://yamahadtx.com/forum/yamaha-dtx-402k-or-dtx450k

originally from Reddit
https://www.reddit.com/r/drums/comments/akv5y5/yamaha_dtx_402k_or_dtx450k/

They do it so they can come back and re-edit the post with loads of spam links.

David wrote:

OP just copied a post from this forum,
https://yamahadtx.com/forum/yamaha-dtx-402k-or-dtx450k

originally from Reddit
https://www.reddit.com/r/drums/comments/akv5y5/yamaha_dtx_402k_or_dtx450k/

They do it so they can come back and re-edit the post with loads of spam links.

That's a pity because I spent some time writing up my answer in the hopes that it would be helpful. Thanks for pointing this out.

Anyway, I sincerely hope that my answer will be of some benefit to somebody.

Yeah - there's loads of spammers on here.

They post something they've copied from somewhere (here or Redit are popular). Then come back, edit the post and stuff a load of spam links in.

Unfortunately, Yamaha doesn't give a sh*t about its customers so despite years of complaining - and offering to help - they do nothing.

So, it's down to a few good souls to weed out the cr*p and help the genuine users - WITH NO THANKS FROM USELESS YAMAHA.