Selling Bitcoin (BTC) to fill your altcoin portfolio could be a bad decision for you, because currently the price performance of altcoins is also affected by Bitcoin (BTC) itself. If Bitcoin (BTC) goes down, then the performance of your altcoin portfolio will also go down, as simple as that. So, it would be better if you rethink your plan. If you still want it, just do it, all the risks, all the decisions are on you, mate.
Greediness and lack of patience is what normally push people to this kind of decision. They often believe altcoin could make 100x with minutes and this can't happen with Bitcoin. But such people have forgotten the risk involved in investing in altcoin.
I never blame anyone for being greedy, because it's human nature. It's just that making choices at the wrong time can make things even worse. One of them is changing the portfolio from mostly Bitcoin (BTC) to altcoins when the market is consolidating, instead of getting the expected profit, because it could be the opposite.
Look at how Bitcoin (BTC) is doing right now, it’s back down below $80K, and it’s not a wise choice to move into altcoins.