I'm talking about taking margin upfront as long as
tradable balance (aka leveraged free margin) allows
to cover the expected swap interest.
Suppose i'm holding a fully leveraged position (can't place margin orders),
knowing that i will be closing it and reentering the market at the later time.
Hence i'd like to secure some margin right away, while rates are still relatively low.
RIght now i have to place multiple tiny swap bids, clogging the order book and everything.
Or is there any other reasons why taking more margin than tradable bl isn't possible atm?
Essentially this is leveraging for swaps. I.e. the same 2.5:1 limit can be applied or not.
Okay, so you mean to take a swap before you need it, at a time when you're not yet able to use it, so that it's reserved at a low rate for when you want it?
I don't know; I suspect that's not something the system will let you do, but I don't see what the harm would be in allowing it. Might have the potential to be abused by someone seeking to manipulate the swap rate by taking up the cheap liquidity without any intent of ever using it - being able to keep up the fee payments is a much lower bar than having enough funds to back up a margin trade.
Although, if you want to take advantage of the cheap swaps that are available, you should be able to 'refinance' by cancelling your existing swap; it'll automatically take the cheapest offer to replace it.