It would have made a lot of difference. Germany likely would not have been able to take the Sudetenland, due to Czechoslovakia's advanced fortification system and nearly equal military force. Not only that, but Czechoslovakia had the advantage of having almost all of its borders be in mountains, making an invasion more difficult. It had a treaty with the Soviet Union as well, and they promised that they would come to Czechoslovakia's aid if France went through with their obligation.

The Panzer IIIs and IVs used to invade France so quickly were not available in 1938 (Czechoslovakia actually accounted for around 15% of Nazi Germany's tank production after it was annex, so appeasement really just let Hitler rearm faster than the allies could). The Panzer Is and IIs were outclassed by the French heavy tanks and even the Czech LT-35s due to inferior armor and gun power (The Mark I panzer didn't even have a cannon, it just had mounted machine guns).

Germany had a few divisions stationed in Prussia and the east along the Polish border, so the available 44 divisions Germany had for the Czechoslovak campaign were faced against 42 Czech divisions, and including France (which was obligated to come to Czechoslovakia's aid because of the 1924 treaty) they overwhelmingly outnumbered the Germans in both infantry and armor. And this isn't even considering British and Soviet forces.

Germany had only allocated nine total infantry divisions on the French border, which would have been easily overwhelmed by the entirety of the French Army. The plan was that France would have been able to relieve Czechoslovakia's forces by pushing in from the West, and with little defense in that area, they likely would have gotten pretty far.

Luftwaffe was in a period of rearmament and was nowhere near the strength it had when bombing Britain in the war. France, Britain, Czechoslovakia and the Soviet Union had almost 3 times the number of fighters and more than double the number of first-line bombers. Czechoslovakia's anti-air defenses were strong and considered capable of causing "serious difficulties" to the German fleet.

Now numbers aside, Czechoslovakia had the morale as well. The whole country was united and willing to fight in the coming moments to the Munich Conference. As history has shown, when nearly every single person in a nation is willing to defend their home, its pretty difficult to invade them successfully.

France and Britain were in arguably worse positions after the invasion of Poland, because Germany (with the help of Czech industry and factories) was able to rearm and manufacture much faster. The Munich Agreement also made the USSR lose trust in the West, and with the Molotov-Ribbentrop Pact gave Germany a one front war letting it focus on France.

Now if they had declared after the invasion of Czechoslovakia, I cannot know for sure, but it would have been much worse. Hitler would not have had to worry about Czechoslovakia and again the Soviet Union would have had a worsened opinion of France and Britain. It would have been difficult for the Soviets to intervene anyways, due to the number of states that stood between it and Germany. British land forces were not ready at all during this time, so it would've been very difficult for France to get very far.