Make command in go-ethereum installation?

i am trying to change the source code of geth and I have some doubts.
I need to modify the following sentence in order to admit transactions with more data in them: txMaxSize = 4 * txSlotSize // 128KB
of tx_pool.go file: https://github.com/ethereum/go-ethereum/blob/master/core/tx_pool.go
I have run

git clone https://github.com/ethereum/go-ethereum.git

My doubt is whether i have to modify the file before or after running make geth

Thanks

From the perspective of building the application, you can simply:

git clone $repo

Make modifications to the file. Then

make geth

or

cd cmd/geth/
go build

to build your application. Just running go build will generally be faster for development / testing, but make geth gives more reproducible builds.

I would warn you though, that unless your plan is to make your own network with a separate client that has larger transactions, building Geth with larger transactions will just mean you can create transactions that won't propagate across the network very successfully as other nodes on the network will reject them. Most miners use Geth (or Geth forks) to assemble new blocks, and changing the parameters yourself won't change it for other nodes on the network.