they will travel by night (as well as) by day.句意？括号里能否改为as well？

当然不能改为 as well 了

as well 是放句末的 比如：--they can play PSP.
--Mika can do it as well
（他们能玩PSP-- Mika一样能玩）
as well as 和 as well的意思都不同
前者 是 和……一样好 后者是 和……一样

如果原句想表示日夜兼程的话

改成：they will travel day and night. 即达到效果又显得俚语化，看着很顺眼的

再说一下 as well as 是一个连接结构 前后的句式和短语格式要一致

比如：（动词 v.+名词 n.）+ as well as +（动词 v.+名词 n.）
(形容词adj.+副词adv.) + as well as + (形容词adj. +副词adv.)

我觉得是，他们在夜里也能像白天一样旅行。不能改。