I mean, you can. Most altcoins are short lived anyway, you're better off trying to profit off of them at a say a month or two max, anything longer would just give diminishing returns, well at least for most coins, but hey if they really were good, it wouldn't be too late to invest on it again after at least guaranteeing that you've profited.

I definitely would avoid investing in altcoins for the long term though. I'd only ever know if it was a good investment for one in the future, and judging by the number of new altcoins, I wouldn't really take my chances.