A birthday banner with interchangeable letters
A reusable base banner can take removable letter cards, making it easier to adapt for another birthday.

Separate the base from the lettering
Instead of permanently gluing each letter to a pennant, make a neutral row of base shapes and attach removable letter cards. The base can then serve another name or occasion. The attachment needs to release without damaging it.
Lay out the longest planned message on paper first. Count letters and spaces. A short name takes less room than a full birthday greeting. Fit the overall span to the actual wall rather than letting the first successful pennant dictate everything.
Test one letter at viewing distance
Cut a rectangular or simple pennant-shaped base, perhaps 3 by 4½ inches. Put a broad letter on a smaller card. Hold the two up from the distance at which the banner will be read. Fine lettering and low contrast disappear more readily than they seem to at the worktable.
Use reasonably firm cardstock for the base and lighter stock for the letter if desired. Try a small suitable clip or another removable fastening. Check that the card hangs straight and that the fastener does not leave a damaging mark.
Save templates if cutting letters. If lettering by hand, establish a common baseline. The strokes need not be perfectly identical; consistent height and clear spacing already help readability.
Assemble the complete sequence
Punch two holes near the top of each base, leaving generous edge margins. Thread a light line through both. Two attachment points help prevent the card from turning as freely as it would around a single central hole.
Lay out the complete message and check the spelling. Set the spacing before securing the ends. For a longer name, slightly smaller lettering may work better than crowding pennants until they overlap.
Hang it from suitable points in a dry room. It is lightweight decoration, not a load-bearing line. Keep cords and small clips away from young children and away from flames.
After the celebration, store the letter cards and bases flat, separately. Put frequently used letters in an envelope and note which duplicates you have. Making one extra letter next time is quicker than reconstructing the entire banner, and the reusable base leaves room to change the colors or message later.