The far side of Finland? That’s the Baltic Sea. Sure, there’s a little bit of Sweden, but it’s so far north that there isn’t much rail infrastructure there - certainly little enough that it could quickly be destroyed at the beginning of a war.

The stated reason for the gauge change is "to remove technical obstacles to transporting troops and goods between Finland, Sweden and Norway".

Those few connections in the sparse north of the country are the entire point.

If the supply line is blown up at the beginning of the war then what was the point of switching gauges.

The objective they try to achieve is not to slow down Russia's invasion into Europe, but to stop them at the border by being able to move assets throughout Europe relatively quickly. If they gain a proper foothold and full access to "euro gauge" rails, it's a different fight.

Of course, if it does go that far, tanks and trains can move rolling stock, rip up the tracks, blow up bridges and other infrastructure behind them if they're forced to retreat.

This. I am struggling to see how this is anything other than posturing by politicians. It’s hard to imagine this is strategy devised by military leaders.